NIST-JANAF Thermochemical Tables. I. Ten Organic ...NIST-JANAF Thermochemical Tables. I. Ten Organic Molecules Related to Atmospheric Chemistry Olga Dorofeevaa– Physical and Chemical
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Journal of Physical and Chemical Reference Data 30, 475 (2001); https://doi.org/10.1063/1.1364518 30, 475
NIST-JANAF Thermochemical Tables. I. TenOrganic Molecules Related to AtmosphericChemistryCite as: Journal of Physical and Chemical Reference Data 30, 475 (2001); https://doi.org/10.1063/1.1364518Submitted: 06 September 2000 . Accepted: 16 January 2001 . Published Online: 12 July 2001
O. V. Dorofeeva, Vladimir P. Novikov, and David B. Neumann
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NIST-JANAF Thermochemical Tables. I. Ten Organic MoleculesRelated to Atmospheric Chemistry
Olga Dorofeeva a…
Physical and Chemical Properties Division, Chemical Science and Technology Laboratory,National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Vladimir P. NovikovDepartment of Chemistry, Moscow State University, Moscow 119899, Russia
David B. Neumann b…
Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, Maryland 21250
~Received 6 September 2000; accepted 16 January 2001!
a!Guest Researcher, currently at the Glushko Thermocenter of the RussianAcademy of Sciences, IVTAN Association of the RAS, Izhorskaya St.13/19, Moscow 127412, Russia; Electronic mail: [email protected].
List of Tables1. Ideal gas thermodynamic properties of
bromoacetic acid C2H3BrO2~g! at the standardstate pressure,p°50.1 MPa~Tr5298.15 K). . . . . 481
2. Ideal gas thermodynamic properties ofchloroacetic acid C2H3ClO2~g! at the standardstate pressure,p°50.1 MPa~Tr5298.15 K!. . . . . . 483
3. Ideal gas thermodynamic properties ofoxopropanedinitrile C3N2O~g! at the standard statepressure,p°50.1 MPa~Tr5298.15 K). .. . . . . . . . 487
4. Ideal gas thermodynamic properties of glycolicacid C2H4O3~g! at the standard state pressure,p°50.1 MPa~Tr5298.15 K). . . . . . . . . . . . . . . . . . 491
5. Ideal gas thermodynamic properties of glyoxalC2H2O2~g! at the standard state pressure,p°50.1 MPa~Tr5298.15 K). . . . . . . . . . . . . . . . . . . . 494
6. Ideal gas thermodynamic properties of thecyanooxomethyl radical C2NO~g! at the standardstate pressure,p°50.1 MPa (Tr5298.15 K). . . . . 497
7. Ideal gas thermodynamic properties of oxalicacid C2H2O4~g! at the standard state pressure,p°50.1 MPa (Tr5298.15 K). . . . . . . . . . . . . . . . . 500
8. Ideal gas thermodynamic properties of methylhydroperoxide CH4O2~g! at the standard statepressure,p°50.1 MPa (Tr5298.15 K).. . . . . . . . 503
9. Ideal gas thermodynamic properties of dimethylperoxide C2H6O2~g! at the standard statepressure,p°50.1 MPa (Tr5298.15 K).. . . . . . . . 506
10. Ideal gas thermodynamic properties of diacetylperoxide, C4H6O4~g! at the standard statepressure,p°50.1 MPa (Tr5298.15 K).. . . . . . . . 509
11. Summary of the thermodynamic properties at298.15 K and the standard state pressure,p°50.1 MPa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510
1. Introduction
A large number of biogenic and industrial polutant speciesplay a direct or indirect role in tropospheric smog chemistry.Modeling of the kinetics of tropospheric chemical reactionprocesses often requires thermodynamic data. In the follow-ing, evaluated thermodynamic data for a few smaller organicspecies including some peroxides relevant to smog chemistryand atmospheric chemistry in general are presented.
The ideal gas thermodynamic properties of the polyatomicmolecules were calculated by standard statistical mechanicalmethods in which a rigid-rotor harmonic-oscillator model,modified where appropriate for internal rotations, was as-sumed for each compound. The statistical formulas for ther-modynamic functions are discussed in several textbooks, re-view articles, and reference books.1–6 Molecular andspectroscopic constants needed for the calculations were se-lected from the literature. In a few cases missing data wereestimated by analogy to related compounds. For some mol-ecules, the fundamental frequencies were estimated by nor-mal coordinate calculations using force constants transferredfrom related molecules and the program NCA written byNovikov and Malyshev.7
To evaluate the internal rotational contributions to thethermodynamic functions, the internal rotational partitionfunction was formed by the summation of internal rotationalenergy levels for each rotor. These energy levels were ob-tained by the diagonalization of the one dimensional Hamil-tonian using a potential function of the form
V~w!51
2 (n
Vn~12cosnw!, ~1!
wherew is the internal rotational angle. The method of gen-erating the internal rotation energy levels has been describedby Lewis et al.8,9 The constant required to generate the in-ternal rotational energy levels for each rotor is the internalrotational constant~F ! or reduced moment of inertia of therotating group (I r). Where available, theVn terms and inter-nal rotational constant were taken from spectroscopic data. Ifthe F value was unavailable, it was calculated from the re-duced moment of inertia with the relationship
F5h/8p2cIr . ~2!
The value ofI r was calculated using molecular structuralparameters with a computer program based on a method ofcalculating the reduced moments of inertia developed byPitzer and Gwinn.10,11
A molecular model of an equilibrium mixture oftransandcis isomers was employed for calculating the thermodynamicfunctions of glyoxal.4,12,13This method uses the enthalpy dif-ference between the two conformers to calculate the equilib-rium mole fraction of each species. From these data andthermodynamic functions of two conformers, values of ther-modynamic functions were calculated, allowing for the mix-ing of two conformers.
The sources of uncertainties in the calculated thermody-namic functions arise from uncertainties in the molecular
476476 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
constants used in the calculations as well as deviations fromthe rigid-rotor harmonic-oscillator model. In this work theuncertainties in the thermodynamic functions were estimatedby the procedure developed by Gurvichet al.6 This approachpredicts the uncertainties in the thermodynamic functionsS°(T) andCp°(T) for simple molecules such as C3N2O rea-sonably well. For molecules with one or more internal rota-tions, the additional uncertainties due to deviations from therigid-rotor harmonic-oscillator model are difficult to assess.The largest uncertainty probably arises from the anharmonic-ity of the asymmetric torsion. This will have little effect atroom temperature but may be significant at the higher tem-peratures. The total estimated uncertainties in the thermody-namic functionsS°(T) and Cp°(T) in the range between298.15 and 2000 K are given in the discussions for eachmolecule.
Based on the selected values of the molecular constants,the ideal gas thermodynamic functions, heat capacity,Cp°(T), entropy, S°(T), enthalpy @H°(T)2H°(298.15 K)#, and the Gibbs energy function$2@G°(T)2H°(298.15 K)#/T%, have been calculated forselected temperatures up to 2000 K at the standard state pres-sure,p°50.1 MPa.~In the tables that follow in a few casesexcited electronic states have been factored into the calcula-tions; the energy of an electronic state relative to the groundelectronic state is given as«G ; the degeneracy of electronicstates are referred to in these tables as the ‘‘quantumweight,’’ gG.) The enthalpy of formation values@D fH°(298.15 K)# were selected by analyzing experimentalstudies which may result in the enthalpies of formation de-termination. In the absence of experimental data, theD fH°(298.15 K) values were estimated by approximatemethods accepted as standard for organic molecules andradicals.14,15
The calculated values of the enthalpy difference,@H°(T)2H°(298.15 K)#, and entropy,S°(T), of the ideal gas were
combined with values of the enthalpies and entropies of theelements in their reference states to derive values of enthalpyof formation (D fH°), Gibbs energy of formation (D fG°),and the logarithm of the equilibrium constant of formation(logKf°) of the substances as a function of temperature overthe range of 0–2000 K.
Values used here of@H°(T)-H°(298.15 K)# and S°(T)for the elements in their reference states@H2~g!, C~cr, graph-ite!, O2~g!, N2~g!, F2~g!, Cl2~g!, and Br2~cr,liq,T,332.503 K) and Br2~g,T.332.503 K] are those given inthe JANAF Thermochemical Tables.5
References
1K. S. Pitzer,Quantum Chemistry~Prentice–Hall, Englewood Cliffs, NJ,1953!.
2J. G. Aston and J. J. Fritz,Thermodynamics and Statistical Thermodynam-ics ~Wiley, New York, 1959!.
3G. N. Lewis, M. Randall, K. S. Pitzer, and L. Brewer,Thermodynamics,2nd ed.~McGraw–Hill, New York, 1961!.
4S. G. Frankiss and J. H. S. Green,Chemical Thermodynamics~TheChemical Society, London, 1973!, Vol. 1, Chap. 8, pp. 268–316.
5M. W. Chase, Jr., C. A. Davies, J. R. Downey, Jr., D. J. Frurip, R. A.McDonald, and A. N. Syverud,JANAF Thermochemical Tables, 3rd ed.@J. Phys. Chem. Ref. Data14, Suppl. 1~1985!#.
6L. V. Gurvich, I. V. Veyts, and C. B. Alcock,Thermodynamic Propertiesof Individual Substances, 4th ed.~Hemisphere, New York, 1989!, Vol. 1,Part 1.
7V. P. Novikov and A. I. Malyshev, Zh. Prikl. Spektrosk.33, 545 ~1980!.8J. D. Lewis, T. B. Malloy, Jr., T. H. Chao, and J. Laane, J. Mol. Struct.12,427 ~1972!.
9J. D. Lewis and J. Laane, J. Mol. Spectrosc.65, 147 ~1977!.10K. S. Pitzer and W. D. Gwinn, J. Chem. Phys.10, 428 ~1942!.11K. S. Pitzer, J. Chem. Phys.14, 239 ~1946!.12K. S. Pitzer, J. Chem. Phys.5, 473 ~1937!.13J. G. Aston and G. Szasz, J. Chem. Phys.14, 67 ~1946!.14N. Cohen and S. W. Benson, Chem. Rev.93, 2419~1993!.15D. R. Stull, E. G. Westrum, Jr., and G. C. Sinke,The Chemical Thermo-
dynamics of Organic Compounds~Krieger, Malabar, FL, 1987!.
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J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
2. Bromoacetic Acid, CH 2Br—COOH
Bromoacetic acid (C2H3BrO2) Ideal gas Mr5138.9485D fH°(0 K)52364.663.1 kJ mol21
S°(298.15 K)5337.065.0 J K21 mol21 D fH°(298.15 K)52383.563.1 kJ mol21
Product of moments of inertia:I AI BI C528 1783102117 g3 cm6.
2.1. Enthalpy of Formation
The recommended value of enthalpy of formation ofgaseous bromoacetic acid,2(383.563.1) kJ mol21, wasobtained by Lagoaet al.1 from experimental measurements.This value is the sum of the enthalpy of formation ofbromoacetic acid in the crystalline state,D f H°(C2H3BrO2,
and the enthalpy of sublimation,DsubH°~C2H3BrO2)5(83.5062.95) kJ mol21, determined from Knudseneffusion experiments. Note that the recommended value isclose to the value predicted by the method of groupequations:2
478478 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
D fH°~CH2Br–COOH!
5D fH°~CH2Cl–COOH!1D fH°~CH2Br–CH3!
2D fH°~CH2Cl–CH3!5~2427.6!1~261.9!
2~2112.1!52377.4 kJ mol21
~theD fH° values for CH2BrCH3, and CH2ClCH3 were takenfrom compilation by Pedley,3 for CH2ClCOOH—from Ref.1!. A somewhat lower estimate of the enthalpy of formationof bromoacetic acid,2~39566! kJ mol21 was given by Liaset al.4
2.2. Heat Capacity and Entropy
From their microwave study, van Eijcket al.5 determinedthe rotational constants of three isotopic species(CH2
79BrCOOH, CH281BrCOOH, and CH2
79BrCOOD!.Although no complete structure could be evaluated from theavailable data, the substitution coordinates of the Br atomand the carboxyl H atom were consistent only with thetransstructure with respect to the atoms Br—C—C—O—H. Thisconformation is identical to lowest-energy form of chloro-acetic acid named ascis-synbecause ofcis configuration forOvC—O—H and Cl—C—CvO groups. Thecis structurewith respect to the atoms Br—C—C—O—H was obtainedby Chenet al.6 from ab initio calculation. However, the ge-ometry of chloroacetic acid calculated by Chenet al.6 wasalso not consistent with that determined from experimentalstudies. The trans structure with respect to the atomsBr—C—C—O—H ~Cs symmetry! is accepted in this workfor lowest-energy conformer of bromoacetic acid in accordwith the microwave data.5 The isotope-weighted value of theproduct of the principal moments of inertia of bromoaceticacid is calculated in this work from the rotational constantsfor CH2
79BrCOOH and CH281BrCOOH.5 Structural param-
eters given above are those estimated by comparison withstructural parameters of CH3COOH,7 CH2ClCH3,
8
CH2ClCOOH,9 and CH2BrCH3.10 These structural param-
eters yield values for the rotational constants which are1.2%–1.6% different from the observed values used in thecalculations. The difference has a negligible effect on thethermodynamic functions.
There is no information on other stable conformers of bro-moacetic acid arising from internal rotation around the C—Cbond. van Eijcket al.5 could only conclude that thegaucheconformation, if present, is not significantly higher in energythan thetransconformation. Their rough estimate of the tor-sional frequency, 47 cm21, may be compared with 62 cm21
for chloroacetic acid.11 As in the case of chloroacetic acid,the simple potential,
V~w!5 12V3~12cos 3w!,
wherew is the Br—C—CvO torsional angle, is used in thiswork to calculate the internal rotational contributions to thethermodynamic functions of bromoacetic acid. The barrierheight for the rotation about the C—C bond is practically thesame in CH2ClCH3 and CH2BrCH3 molecules.12,13 For thatreason, the value ofV3 for bromoacetic acid was accepted tobe the same as that for chloroacetic acid. The value of thereduced moment of inertia for the CH2Br top was derivedfrom structural parameters adopted in this work~see above!.
Vibrational spectra of bromoacetic acid were investigatedonly for a solid phase.14–17These vibrational assignments areincomplete and it may be expected that they are much dif-ferent from a gaseous spectrum as in the case of chloroaceticacid. Fundamental frequencies of gaseous bromoacetic acidwere estimated in this work by normal coordinate calcula-tions using the force constants transferred from related com-pounds. Simplified force fields for CH3COOH, CH2ClCH3,CH2BrCH3, and CH2ClCOOH were determined using ex-perimental vibrational assignments for these molecules.18–21
37 force constants were used to calculate the vibrational fre-quencies of bromoacetic acid:
f O—H 7.092 f wag~CvO! 0.310 f C—C,C—C—H 0.199f C—H 4.998 f tors~C—O! 0.183 f C—C,C—C—O 20.425f CvO 14.076 f tors~C—C! 0.028 f C—C,C—C—Br 20.017f C—C 4.101 f C—H,C—H 0.061 f C—C,OvC—C5 f C—C,OvC—O 1.250f C—O 3.891 f C—H,C—C 0.332 f C—O,C—O—H 0.041f C—Br 3.531 f C—H,C—Br 20.402 f C—O,C—C—O 0.296f H—C—H 0.274 f C—C,C—Br 0.377 f C—O,OvC—C5 f C—O,OvC—O 0.605f C—C—H 0.793 f C—C,C—O 0.693 f C—Br,H—C—Br 0.148f C—O—H 0.424 f CvO,C—O 2.221 f C—Br,C—C—Br 0.044f C—C—O 2.465 f CvO,C—C 1.660 f C—H,H—C—Br 20.533f H—C—Br 0.547 f CvO,C—C—O 21.365 f C—H,H—C—H 20.184f C—C—Br 1.042 f CvO,OvC—C5 f CvO,OvC—O 0.687 f C—H,C—C—H 0.216f OvC—C5 f OvC—O 2.312
479479NIST-JANAF THERMOCHEMICAL TABLES
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
~stretching and stretch–stretch interaction constants are inunits of mdyn/Å; bend, wagging, and torsion constants are inunits of mdyn Å; stretch–bend interaction constants are inunits of mdyn!. These constants were transferred fromCH3COOH and CH2BrCH3 molecules with corrections madeby analyzing the trends in force constants of moleculesCH3COOH, CH2ClCH3, and CH2ClCOOH.
The uncertainties in the calculated thermodynamic func-tions ~Table 1! may reach~3–6! J K21 mol21 for Cp°(T) and~5–12! J K21 mol21 for S°(T). They are caused by the un-certainties in the adopted vibrational frequencies and the ap-proximate treatment of internal rotation.
Ideal gas thermodynamic properties of bromoacetic acidhave not been reported previously.
2.3. References
1A. L. C. Lagoa, H. P. Diogo, M. Pilar Dias, M. E. Minas da Piedade, L.M. P. F. Amaral, M. A. V. Ribeiro da Silva, J. A. Martinho Simo˜es, R. C.Guedes, B. J. Costa Cabral, K. Schwarz, and M. Epple, Chem. Eur. J.7,483 ~2001!.
2D. R. Stull, E. F. Westrum, and G. C. Sinke,The Chemical Thermody-namics of Organic Compounds~Krieger, Malabar, FL, 1987!; see also the‘‘difference method,’’ N. Cohen, and S. W. Benson, Chem. Rev.93, 2419~1993!.
3J. B. Pedley,Thermochemical Data and Structures of Organic Com-pounds~Thermodynamics Research Center, College Station, TX, 1994!,Vol. I.
4S. G. Lias, J. E. Bartmess, J. F. Liebman, J. L. Holmes, R. D. Levin, andW. G. Mallard, J. Phys. Chem. Ref. Data17, Suppl. 1~1988!.
5B. P. van Eijck, H. A. Dijkerman, and J. Smits, J. Mol. Spectrosc.73, 305~1978!.
6L.-T. Chen, G.-J. Chen, and X.-Y. Fu, Chin. J. Chem.13, 10 ~1995!.7B. P. van Eijck, J. van Opheusden, M. M. M. van Schaik, and E. vanZoeren, J. Mol. Spectrosc.86, 465 ~1981!.
8M. Hayashi and T. Inagusa, J. Mol. Struct.220, 103 ~1990!.9J. L. Derissen, and J. M. J. M. Bijen, J. Mol. Struct.29, 153 ~1975!.
10T. Inagusa and M. Hayashi, J. Mol. Spectrosc.129, 160 ~1988!.11B. P. van Eijck, A. A. J. Maagdenberg, and J. Wanrooy, J. Mol. Struct.22,
61 ~1974!.12J. R. Durig, W. E. Bucy, L. A. Carreira, and C. J. Wurrey, J. Chem. Phys.
60, 1754~1974!.13J. Gripp, H. Dreizler, and R. Schwarz, Z. Naturforsch. A40, 575 ~1985!.14J. E. Katon, T. P. Carll, and F. F. Bentley, Appl. Spectrosc.25, 229
~1971!.15J. E. Katon and D. Sinha, Appl. Spectrosc.25, 497 ~1971!.16J. E. Katon and R. L. Kleinlein, Spectrochim. Acta A29, 791 ~1973!.17P. F. Krause, J. E. Katon, and R. W. Mason, J. Phys. Chem.82, 690
~1978!.18H. Hollenstein and H. H. Gu¨nthard, J. Mol. Spectrosc.84, 457 ~1980!.19S. Suzuki and A. B. Dempster, J. Mol. Struct.32, 339 ~1976!.20S. Suzuki, J. L. Bribes, and R. Gaufres, J. Mol. Spectrosc.47, 118~1973!.21 J. Nieminen, M. Pettersson, and M. Ra¨sanen, J. Phys. Chem.97, 10925
~1993!.
480480 DOROFEEVA, NOVIKOV, AND NEUMANN
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3. Chloroacetic Acid, CH 2Cl—COOH
Chloroacetic acid (C2H3ClO2) Ideal gas Mr594.4975D fH°(0 K)52416.061.0 kJ mol21
S°(298.15 K)5325.965.0 J K21 mol21 D fH°(298.15 K!52427.661.0 kJ mol21
a 1aInstead of torsional moden18562 cm21, the contributions due to theinternal rotation about C—C bond were calculated from the potentialV(w)5 1
2V3(12cos 3w), where w is the torsional angle andV3
5450 cm21.
CH2Cl top: Reduced moment of inertia,I r52.4514310239 g cm2, Symmetry number,sm51.
Geometry
r (C—H!51.0960.02 År (O—H!50.9760.015 Å/C—CvO5126.160.5°/C—C—O5110.660.4°/C—C—Cl5112.560.4°/C—C—H5109.5~assumed!
r (C—C!51.50860.006 Å /H—C—H5109.5~assumed!r (CvO!51.22360.004 Å /C—O—H5105.861.1°r (C—O!51.35260.005 Å w(OvC—C—Cl)50.0°r (C—Cl!51.77860.005 Å w(OvC—O—H)50.0°
Rotational constants in cm21:A050.350 738 B050.078 433 C050.064 913
Product of moments of inertia:I AI BI C512 2843102117 g3 cm6.
3.1. Enthalpy of Formation
The recommended value of the enthalpy of formation ofgaseous chloroacetic acid at 298.15 K is the sum of the en-thalpy of formation of thea form of the solid and the en-thalpy of sublimation both at 298.15 K. The value ofD fH°(298.15 K,a-cr)52(509.7460.49) kJ mol21 is fromthe work of Lagoaet al.1 who measured the enthalpy ofcombustion of thea form of the solid with a rotating bombcalorimeter. Their result is in agreement with the resultD fH°(298.15 K,cr)52(510.568.3) kJ mol21 of Smithet al.2 from their re-evaluation of earlier static bomb calo-rimetry measurements.3
The enthalpy of sublimation,DsubH°(298.15 K)5(82.1960.92) kJ mol21, used here is also from Lagoaet al.,1 and isderived from vapor pressures of the solid obtained fromKnudsen effusion experiments. This value is supported byapplication of Hess’s law where the enthalpy of sublimationis the sum of five processes at the standard pressure of 1 bar.Thus,
DsubH° ~298.15 K!
5@H°~cr,334.8 K!2H°~cr,298.15 K!#
1D fusH°~334.8 K!1@H°~1,462 K!2H°~1,334.8 K!#
1DvapH°~462 K!2@H°~g,462 K!
2H°~cr,298.15 K!#580.962.3 kJ mol21.
The first and third terms@H°(T2)2H°(T1)#'Cp°(cr)3DT are (3.960.1) and (21.660.5) kJ mol21, respectively,based onCp°(cr)5(106.762.0) J K21 mol21 from differen-tial scanning calorimetery~DSC! measurements1 andCp°(1)5(168.964.0) J K21 mol21 from Pickering.4 @Thisvalue ofCp°(cr) differs significantly from the average valueof 144 J K21 mol21 over the range of 288–318 K reported inPickering4 and adopted in NIST Chemistry WebBook5 andDonalski and Hearing.6 The value ofCp°(1)5179.9 J K21
mol21 from Urazovskii and Sidorov7 was not used.#D fusH°(334.8 K)516.360.7 kJ mol21 from DSCmeasurements1 while DvapH°(462 K)5(54.562.0) kJ mol21
482482 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
is derived from vapor pressure data over a temperature rangefrom 385.45 K to the normal boiling point.9,10 @Other valuesof D fusH°(334.8 K) are 16.3 kJ mol21 from Pickering4 and12.3 kJ mol21 from Acree.8# The value @H°(g,462 K)2H°(cr,298.15 K)#5(15.460.7) kJ mol21 is interpolatedfrom Table 2 of the present work. This corrects the estimateDsubH°(298.15)5(75.364.2) kJ mol21 by Cox andPilcher5,6,11 based onD fusH°(334 K)519.4 kJ mol21 fromSteiner and Johnson12 and DvapH°(462 K)554.5 kJ mol21
mentioned above. Cox and Pilcher also use Hess’s law, butassume that the values ofCp° for the gas, liquid, and solidphases are equal.
3.2. Heat Capacity and Entropy
According to the experimental13–18 and theoretical15,17–19
studies, the lowest-energy conformer of chloroacetic acid
(CH2Cl—CO—OH) has thecis-synstructure~Cs symmetry!with the cis configuration for the carboxylic group and withthe chlorine atom lying in the carboxylic plane eclipsed withthe carbonyl group. The second more stable form corre-sponds to thecis-gauchestructure with a Cl—C—CvOangle of;130° ~C1 symmetry!. This form differs fromcis-synby internal rotation of the CH2Cl group about the C—Cbond. Structural parameters of the most stable conformer ofchloroacetic acid were determined by gas phase electrondiffraction.14 These parameters are in good agreement withresults fromab initio18,19 and molecular mechanics15 calcu-lations. In this work, the product of the principal moments ofinertia for the most stablecis-synconformer of chloroaceticacid was calculated using rotational constants determinedfrom the microwave study.13 Structural parameters givenabove are those obtained from the electron diffraction
TABLE 2. Ideal gas thermodynamic properties of chloroacetic acid C2H3ClO2(g) at the standard state pressure,p°50.1 MPa~Tr5298.15 K!
study.14 These parameters reproduce the product of the prin-cipal moments of inertia calculated above within 3%.
Three conformations with respect to internal rotationaround the C—C bond were found from an electron diffrac-tion investigation,14 namely, 56% of acis-synconformation,30% of a cis-gaucheconformation with the CH2Cl grouprotated 131° from the former position, and the remaining14% of acis-gaucheconformation with 79° rotation of theCH2Cl group. Three conformers of chloroacetic acid wereidentified by vibrational spectroscopy.15–18 Two of themwere cis-synand cis-gauchein agreement with the electrondiffraction data. The third stable form was found to have thetrans structure, in which the carboxylic hydrogen atom is inthe transposition with respect to the CvO bond.Transcon-formers arise from rotation of the OH group about the C—Obond. Ab initio calculations17,18 and molecular mechanicsstudies15 strongly suggest that the third stable form should bethe trans form. The barrier height for the rotation of the OHgroup around the C—O bond is predicted to be 1700–3500cm21.16–18Due to the height of this barrier and the tempera-ture range of the present tabulation, this internal rotation wasignored in this work.
Two cis conformers with respect to internal rotation aboutthe C—C bond were considered in this work: thecis-synconformer ofCs symmetry and two enantiomeric forms ofcis-gaucheconformer ofC1 symmetry. The observed dataand the calculations14,16–18 consistently predict a slight en-ergy preference for thecis-synform and a small barrier of~400–450! cm21 for its interconversion. The simple potential
V~w!5 12V3~12cos 3w!,
wherew is the Cl—C—CvO torsional angle, is used herefor a very approximate calculation of the internal rotationalcontributions to the thermodynamic functions of chloroaceticacid. The value of the reduced moment of inertia for theCH2Cl top was derived from the electron diffraction struc-tural parameters.14
Vibrational spectra of chloroacetic acid were studied in theliquid and solid phases,15,20,21in the vapor22 and matrix.16,18
The fundamental frequencies adopted in this work are thosederived by Nieminenet al.18 from matrix isolation infraredspectra (n1 ,n3–n5 ,n7 ,n8 ,n9 ,n15–n17) and ab initio calcu-lation (n2 ,n6 ,n10–n14). These frequencies are in goodagreement with results of normal coordinate analysis,22 mo-lecular mechanics,15 and ab initio17 calculations. The valuefor the torsional frequency,n18, was estimated from the mi-crowave spectrum13 and it coincides with the value calcu-lated by theab initio method.18
The uncertainties in the calculated thermodynamic func-tions~Table 2! may amount to as much as~3–5! J K21 mol21
for Cp°(T) and 5–10 J K21 mol21 for S°(T). They arecaused by the uncertainties in the adopted vibrational fre-quencies and the approximate treatment of the internal rota-tion.
Thermodynamic properties of chloroacetic acid were cal-culated earlier by Banerjee23 using molecular constantsknown at that time. A value for the barrier height of;1750
cm21 was adopted for calculating the internal rotation con-tributions of the CH2Cl and OH groups. The difference be-tween the values ofCp°(T) andS°(T) given here and thoseby Banerjee23 amounts to 57 and 35 J K21 mol21, respec-tively. Such a difference could not be due to the discrepancyin molecular constants used. The calculation of Banerjee23
seems to be in error. The rough estimate by the method ofgroup equations,
Cp°~CH2Cl—COOH!
5Cp°~CH3—COOH!1Cp°~CH2Cl—CH3!
2Cp°~CH3—CH3!
563.4162.6252.5573.5 JK21 mol21,
is close to the value obtained in this work~78.8 J K21 mol21!and is very different from the value of Banerjee23 ~136.0J K21 mol21!. The calculation of Banerjee23 is reproduced inthe reference book of Frenkelet al.24
3.3. References
1A. L. C. Lagoa, H. P. Diogo, M. Pilar Dias, M. E. Minas da Piedade, L.M. P. F. Amaral, M. A. V. Ribeiro da Silva, J. A. Martinho Simo˜es, R. C.Guedes, B. J. Costa Cabral, K. Schwarz, and M. Epple, Chem. Eur. J.7,483 ~2001!.
2L. Smith, L. Bjellerup, S. Krook, and H. Westermark, Acta Chem. Scand.7, 65 ~1953!.
3E. Schjanberg, Z. Phys. Chem. Abt. A172, 197 ~1935!.4S. U. Pickering, J. Chem. Soc.67, 664 ~1895!.5NIST Chemistry WebBook, NIST Standard Reference Database Number69, edited by W. G. Mallard and P. J. Lindstrom~National Institute ofStandards and Technology, Gaithersburg, MD, November 1998! ~http://webbook.nist.gov/chemistry!.
6E. S. Domalski and E. D. Hearing, J. Phys. Chem. Ref. Data25, 1 ~1996!.7S. S. Urazovskii and I. A. Sidorov, Dokl. Akad. Nauk SSSR70, 859~1950!.
8W. E. Acree, Jr., Thermochim. Acta189, 37 ~1991!.9R. R. Dreisbach and S. A. Shrader, Ind. Eng. Chem.41, 2879~1949!.
10D. R. Stull, Ind. Eng. Chem.39, 517 ~1947!.11J. D. Cox and G. Pilcher,Thermochemistry of Organic and Organometal-
lic Compounds~Academic, London, 1970!.12L. E. Steiner and J. Johnston, J. Phys. Chem.32, 912 ~1928!.13B. P. van Eijck, A. A. J. Maagdenberg, and J. Wanrooy, J. Mol. Struct.22,
61 ~1974!.14J. L. Derissen and J. M. J. M. Bijen, J. Mol. Struct.29, 153 ~1975!.15R. Fausto and J. J. C. Teixeira-Dias, J. Mol. Struct.144, 225 ~1986!.16A. Kulbida and A. Nosov, J. Mol. Struct.265, 17 ~1992!.17R. Fausto, J. J. C. Teixeira-Dias, and F. P. S. C. Gil, J. Chem. Soc.,
Faraday Trans.89, 3235~1993!.18J. Nieminen, M. Pettersson, and M. Ra¨sanen, J. Phys. Chem.97, 10925
~1993!.19K. E. Edgecombe and R. J. Boyd, Can. J. Chem.62, 2881~1984!.20J. R. Barcelo, M. P. Jorge, and C. Otero, J. Chem. Phys.28, 1230~1958!.21R. J. Jakobsen and J. E. Katon, Spectrochim. Acta A29, 1953~1973!.22L. I. Kozhevina, V. M. Belobrov, V. A. Panichkina, and E. V. Titov, Zh.
Strukt. Khim.20, 405 ~1979!.23S. C. Banerjee, Br. Chem. Eng.14, 671 ~1969!.24M. Frenkel, G. J. Kabo, K. N. Marsh, G. N. Roganov, and R. C. Wilhoit,
Thermodynamics of Organic Compounds in the Gas State~Thermodynam-ics Research Center, College Station, TX, 1994!, Vol. I, p. 341.
484484 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
4. Oxopropanedinitrile, NC ACOACN
Oxopropanedinitrile (C3N2O) Ideal gas Mr580.0458D fH°(0 K)5246.566.4 kJ mol21
S°(298.15 K)5310.061.0 J K21 mol21 D fH°(298.15 K)5247.566.4 kJ mol21
r ~CvO!51.20460.005 År ~C–C!51.46160.005 År ~CwN!51.15960.015 Å/C—C—C5114.760.5°/C—CwN5179.260.5°
Rotational constants in cm21:A050.225 529 B050.097 556 C050.067 980.
Product of moments of inertia:I AI BI C514 6663102117 g3 cm6.
4.1. Enthalpy of Formation
The recommended value of enthalpy of formation of oxo-propanedinitrile is based on calorimetric measurements byvon Glemser and Ha¨usser1 as evaluated by Cox and Pilcher.2
4.2. Heat Capacity and Entropy
Spectroscopic,3–10 electron diffraction,11 andtheoretical12–20 investigations have shown that oxopropane-dinitrile, CO~CN!2, is planar in its ground electronic stateX 1A1 and belongs to theC2n symmetry group. In this work,the product of the principal moments of inertia of CO~CN!2
was calculated using the rotational constants determined bymicrowave spectroscopy.4 In the absence of isotopic data, aunique set of geometrical parameters cannot be obtainedfrom the microwave spectrum. Structural parameters givenabove arer e parameters determined by combining the resultsof electron diffraction, microwave spectroscopy, andab ini-tio calculations.20 These parameters give values for rotationalconstants which are only 0.3%–0.9% different from the ob-served values. The C—C[N chain appears to be nearly lin-
ear, the deviation from linearity being 0.8°. A small inwardbend ~0.5°–2°! was also found by ab initiocalculations12,13,19 but is contradicted byab initio calcula-tions of Tyrrell15 where the C—C[N is bent outwards by1.2°.
Vibrational spectra of oxopropanedinitrile were studied inthe gas, liquid, and solid phase5–10 but there are still severaluncertainties in the assignment of the fundamentals. The vi-brational frequencies accepted in this work are those as-signed by Milleret al.9 from infrared and Raman spectra ofgaseous and liquid oxopropanedinitrile. Their assignmentwas supported byab initio calculation.15
According to the semiempirical calculation,21 the excitedelectronic states of CO~CN!2 lie above 24 000 cm21. Theyare not taken into account in the calculation of thermody-namic functions.
The uncertainties in the calculated thermodynamic func-tions ~Table 3!are estimated to be~1–2! J K21 mol21 forCp°(T) and ~1–2.5! J K21 mol21 for S°(T).
Thermodynamic properties of CO~CN!2 were calculatedearlier by Natarajan and Rajendran22 using electron diffrac-
485485NIST-JANAF THERMOCHEMICAL TABLES
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
tion structural parameters11 and the vibrational assignment ofBates and Smith.8 The numerical data in the four columns ofthe table of thermodynamic functions in Natarajan andRajendran22 are transposed. Moreover, these functions do notcorrespond to the molecular constants used by the authors.The difference between theCp°(T) andS°(T) values givenhere and those by Natarajan and Rajendran22 amounts to 20J K21 mol21 and could not be due to the discrepancy in mo-lecular constants used.
4.3. References
1O. von Glemser and V. Ha¨usser, Z. Naturforsch. B3, 159 ~1948!.2J. D. Cox and G. Pilcher,Thermochemistry of Organic and Organometal-lic Compounds~Academic, London, 1970!; see also J. B. Pedley,Ther-mochemical Data and Structures of Organic Compounds~Thermodynam-ics Research Center, College Station, TX, 1994!, Vol. I.
3J. F. Westerkamp, Bol. Acad. Nacl. Cienc. Argen.42, 191 ~1961!.4R. M. Lees, Can, J. Chem.49, 367 ~1971!.5A. Tramer and K. L. Wierzchowski, Bull. Acad. Pol. Sci., Classe III5,411 ~1957!.
6A. Tramer and K. L. Wierzchowski, Bull. Acad. Pol. Sci., Classe III5,417 ~1957!.
7J. Prochorov, A. Tramer, and K. L. Wierzchowski, J. Mol. Spectorsc.19,45 ~1966!.
8J. B. Bates and W. H. Smith, Spectrochim. Acta A26, 455 ~1970!.9F. A. Miller, B. M. Harney, and J. Tyrrell, Spectrochim. Acta A27, 1003~1971!.
10D. M. Thomas, J. B. Bates, E. R. Lippincott, Indian. J. Pure Appl. Phys.9,969 ~1971!.
11V. Typke, M. Dakkouri, and F. Schlumberger, J. Mol. Struct.62, 111~1980!.
12W. Kosmus, K. Kalcher, and G. D. Fleming, J. Mol. Struct: THEOCHEM89, 317 ~1982!.
13K. Siam, M. Dakkouri, J. D. Ewbank, and L. Scha¨fer, J. Mol. Struct:THEOCHEM 204, 291 ~1990!.
14M. Dakkouri, Struct. Chem.1, 179 ~1990!.15J. Tyrrell, J. Mol. Struct.: THEOCHEM231, 87 ~1991!.16M. Dakkouri, J. Mol. Struct.: THEOCHEM258, 401 ~1992!.17J. Tyrrell, J. Mol. Struct.: THEOCHEM258, 403 ~1992!.18J. L. G. De Paz and M. Yanez, J. Mol. Struct.: THEOCHEM107, 59
~1984!.19M. H. Palmer, J. Mol. Struct.: THEOCHEM200, 1 ~1989!.20J. Demaison, G. Wlodarczak, H. Ru¨ck, K. H. Wiedenmann, and H. D.
Rudolph, J. Mol. Struct.:376, 399 ~1996!.21C. H. Warren and C. Ching, Theor. Chim. Acta30, 1 ~1973!.22A. Natarajan and S. Rajendran, Can. J. Spectorsc.26, 229 ~1981!.
486486 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
5. Glycolic Acid, HO ACH2ACOOH
Glycolic acid (C2H4O3) Ideal gas Mr576.0518D fH°(0 K)52567.9610.0 kJ mol21
S°(298.15 K)5318.665.0 J K21 mol21 D fH°(298.15 K)52583.0610.0 kJ mol21
Molecular constants
Point group:C1 Symmetry number:s51 Number of optical isomers:n52Ground electronic state:X 1A Energy:eX50 cm21 Quantum weight:gX51
TABLE 3. Ideal gas thermodynamic properties of oxopropanedinitrile C3N2O(g) at the standard state pressure,p°50.1 MPa~Tr5298.15 K)
COOH top: Reduced moment of inertia,I r51.9292310239g cm2, Symmetry number,sm51.
Geometry
r (C1—C2!51.49560.006 År (C1—O3!51.34960.006 År (C1vO4!51.21060.006 År (C2—O5!51.40660.004 År (O3—H9!50.98960.019 År (O5—H8!50.95660.003 År (C2—H6,7!51.09760.003 Å
Rotational constants in cm21:A050.356 783 B050.135 128 C050.099 891.
Product of moments of inertia:I AI BI C545553102117 g3 cm6.
Other stable conformers: Point group Symmetry number,s Number of optical isomers,n Energy, cm21
C1 1 2 1200C1 1 2 1300
5.1. Enthalpy of Formation
No experimental or theoretical data on enthalpy of forma-tion of gaseous glycolic acid are known from the literature.The value accepted in this work,D fH° (298.15 K)52(583610) kJ mol21, is based on two estimates by addi-tivity methods.
The first value was estimated by group additivity using theequation
D fH°~HO—CH2—COOH!
5D fH°@O—~H!~C!#1D fH°@C—~H!2~CO!~O!#
1D fH°@CO—~C!~O!#1D fH°@O—~CO!~H!#
5~2158.6!1~233.5!1~2147.3!1~2241.8!
52581.2 kJ mol21
with group values generated by Cohen1 except for the miss-ing value for the@C—~H!2~CO!~O!# group. The latter wasevaluated from values known for related groups:
D fH°@C—~H!2~CO!~O!#
5D fH°@C—~H!2~CO!~C!#
1D fH°@C—~H!~CO!~C!~O!#
2D fH°@C—~H!~CO!~C!2#
488488 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
5~221.8!1~218.8!
2~27.1!5233.5 kJ mol21.
The otherD fH° value of glycolic acid may be predicted bythe method of group equations2 using
D fH°~HO—CH2—COOH!
5D fH°~CH3—COOH!1D fH°~HO—CH2—CH3!
2D fH°~CH3—CH3!
5~2432.8!1~2235.2!
2~283.8!52584.2 kJ mol21.
Values for D fH° for CH3COOH, CH3CH2OH, and C2H6
were taken from a compilation by Pedley.3 A value interme-diate between the above two estimates was assigned to theenthalpy of formation of glycolic acid.
5.2. Heat Capacity and Entropy
From microwave spectroscopic studies,4–6 the lowest-energy structure of glycolic acid was concluded to be ofCs
symmetry with the alcoholic hydroxyl group pointing towardthe carbonyl oxygen of carboxyl group. This structure in-volves the intramolecular bonding between the alcohol hy-drogen and the carbonyl oxygen. With the exception of themethylene hydrogen all the atoms in the molecule werefound to be coplanar. The pathways and energy barriers in-volved in possible conformational interconversions of gly-colic acid were investigated byab initio calculations.7–12
Along with rotamers ofcis-glycolic acid, where the carbonylgroup has thecis conformation with its hydroxyl group, theconformers oftrans-glycolic acid were predicted from theo-retical studies. Based on electron diffraction data13 the sec-ond lowest conformer has been assigned to acis-glycolicacid with hydrogen bonding between two hydroxyl groups.The energy difference between these conformers was foundto be 1470 cm21 based on fitting to the diffraction data.However, this result is in conflict with theoretical data8,10–12
predicting the energy difference for the two lowest conform-ers to be 530–880 cm21. Moreover, it has been shown byGodfreyet al.11 from ab initio calculations and a microwavestudy that the two experimentally observed glycolic acid spe-cies need not necessarily be the two of lowest energy. Theauthors in Ref. 11 have assigned the second conformer de-tected by microwave spectroscopy as thetrans-glycolic acidwith relative energy of;1200 cm21. This conformer wasstructurally quite similar to thetrans-glycolic acid conformerdetected earlier in an infrared matrix isolation study.9
The symmetries and relative stabilities of the conformersof glycolic acid adopted in this work are based on the de-tailed ab initio calculations of Godfreyet al.11 who testedsome of their predictions experimentally. The lowest energy
conformer identified byab initio calculation11 was found tobe theC1 conformer which is a slightly twisted version ofthe Cs from detected by microwave spectroscopy.4–6 A con-former of C1 symmetry exists in two enantiomeric forms,and there is a small barrier~1.5 cm21! between this con-former and its mirror image where the saddle point is ofCs
symmetry. The ground vibrational state energy in these sym-metric double wells may be greater than the height of thesaddle point, in which case the effective structure of the ob-served conformer would closely match theCs conformer ofthe saddle point. It should be noted that the decision betweenassigningCs or C1 symmetry is of great importance for thecalculation of the thermodynamic functions. ForC1 symme-try the termR ln 2 must be added to both the entropy andGibbs energy function because two optically isomeric formsare present.C1 symmetry was accepted in this work as thepoint group of the lowest-energy form of glycolic acid.
The product of the principal moments of inertia for themost stable conformer of glycolic acid was calculated usingthe rotational constants determined from microwave spec-trum investigation.4 Structural parameters given above weredetermined from the microwave spectra of normal and iso-topically substituted species of glycolic acid.5 In general,these geometric molecular parameters are close to those de-termined from electron diffraction analysis13 and ab initiocalculations.7,8,10
According to theab initio calculation of Godfreyet al.11
the C1 conformer, a twisted version ofcis-form with hydro-gen bonding between the hydroxyl groups, is expected to bethe second lowest conformer with relative energy of 693cm21. In this work, the energy profile between two lowest-energy C1 conformers11 was approximated by a potentialenergy function for internal rotation around the C—C bond,
V~w!51
2 (n51
8
Vn~12cosnw!,
wherew is the O4—C1—C2—C5 torsional angle. The eightcoefficients (Vn) in the expansion for this moderately com-plex potential energy function were determined using datafrom the ab initio calculation by Godfreyet al.11 The flatminimum at w50° corresponds to the lowest-energyC1
conformer of glycolic acid. Because of the small barrierheight between its enantiomeric forms~1.5 cm21!, they arenot represented by the above potential and their contributionwas taken into account by adding theR ln 2 to the entropyand Gibbs energy function. The barrier of 1658 cm21 atf5110° separates the lowest-energy conformer from thesecondC1 stable conformer with an energy minimum of 693cm21 at f5155°. There is a barrier of 338 cm21 at w5180° between this conformer and its mirror image. Thevalue of the reduced moment of inertiaI r was calculatedusing the molecular structural parameters of Blom andBauder.5 The next most abundantC1 conformers with rela-tive energies of;1200 and 1300 cm21 ~Goldfrey et al.11!were taken into account in this work ignoring their internal
489489NIST-JANAF THERMOCHEMICAL TABLES
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
rotation and adopting their molecular constants to be thesame as those of the basic conformer. The conformers withenergies of about 2000 cm21 and higher were ignored be-cause of their negligible contribution to the thermodynamicfunctions.
Hollensteinet al.14 have measured the infrared spectra of11 isotopic modifications of glycolic acid isolated in an ar-gon matrix and have evaluated the transferable valence forcefield that reproduced the observed frequencies and isotopicshifts very satisfactorily. The vibrational assignment by Hol-lensteinet al.14 for Cs symmetry is adopted in this work.Fundamentals of glycolic acid calculated by anab initiomethod10 are close to experimental values except for thelow-frequency torsional mode.
The uncertainties in the calculated thermodynamic func-tions ~Table 4! may reach~3–5! J K21 mol21 for Cp°(T) and~5–10! J K21 mol21 for S°(T). They are essentially due tothe approximate treatment of internal rotation in glycolicacid.
Ideal gas thermodynamic properties of glycolic acid havenot been reported previously.
5.3. References
1N. Cohen, J. Phys. Chem. Ref. Data25, 1411~1996!.2D. R. Stull, E. F. Westrum, and G. C. Sinke,The Chemical Thermody-namics of Organic Compounds~Krieger, Malabar, FL, 1987!; see also the‘‘difference method,’’ N. Cohen and S. W. Benson, Chem. Rev.93, 2419~1993!.
3J. B. Pedley,Thermochemical Data and Structures of Organic Com-pounds~Thermodynamics Research Center, College Station, TX, 1994!,Vol. I.
4C. E. Blom and A. Bauder, Chem. Phys. Lett.82, 492 ~1981!.5C. E. Blom and A. Bauder, J. Am. Chem. Soc.104, 2993~1982!.6H. Hasegawa, O. Ohashi, and I. Yamaguchi, J. Mol. Struct.82, 205~1982!.
7M. D. Newton and G. A. Jeffrey, J. Am. Chem. Soc.99, 2413~1977!.8T.-K. Ha, C. E. Blom, and H. H. Gu¨nthard, J. Mol. Struct.; THEOCHEM85, 285 ~1981!.
9H. Hollenstein, T.-K. Ha, and H. H. Gu¨nthard, J. Mol. Struct.146, 289~1986!.
10M. Flock and M. Ramek, Int. J. Quant. Chem.26, 505 ~1992!.11P. D. Godfrey, F. M. Rodgers, and R. D. Brown, J. Am. Chem. Soc.119,
2232 ~1997!.12F. Jensen, Acta Chem. Scand.51, 439 ~1997!.13K. Iijima, M. Kato, and B. Beagley, J. Mol. Struct.295, 289 ~1993!.14H. Hollenstein, R. W. Scha¨r, N. Schwizgebel, G. Grassi, and H. H.
Gunthard, Spectrochim. Acta A39, 193 ~1983!.
490490 DOROFEEVA, NOVIKOV, AND NEUMANN
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TABLE 4. Ideal gas thermodynamic properties of glycolic acid C2H4O3(g) at the standard state pressure,p°50.1 MPa~Tr5298.15 K)
Product of moments of inertia,I AI BI C310117 g3 cm6:
504.42 710.17
Reduced moment of inertia for CHOtop, I r31039 g cm2:
0.8199 0.4807
Symmetry number for CHO top,sm : 1 1
aInstead of torsional moden7 ~126.7 cm21 for trans- and 89.6 cm21 for cis-glyoxal!, the contributions dueto the internal rotation were calculated from the potentialV(w)5 1
2(n516 Vn(12cosnw), where w is the
torsional angle,V151587.6,V251139.5,V35259.0,V452110.9,V5540.0, andV650.0 ~in cm21!. Forthe internal rotational constantB, the Fourier expansion coefficients were usedB5B01(n51
The value ofD fH° ~298.15 K! for glyoxal accepted in thiswork was determined by Fletcher and Pilcher1 from mea-surements of heat of combustion by flame calorimetry. Alower value of 2224.3 kJ mol21 was obtained by Curtisset al.2 from ab initio calculation.
6.2. Heat Capacity and Entropy
It has been shown both spectroscopically3–18 andtheoretically19–35that glyoxal (OvCH—CHvO) undergoesrotational isomerization and exists in two planar,trans andcis, forms. The structure of the more stabletrans conformerhas been determined by a combination of electron diffractionand rotational data.36 As trans-glyoxal has no dipole mo-ment, there is no microwave spectrum, and accurate rota-tional constants for the ground state can only be obtained byrotational analysis of infrared or electronic absorption bands.The values obtained for the rotational constants oftrans-glyoxal4,5,13,14,37 are in good agreement with eachother. Using the rotational constants for the five isotopic spe-cies, Birsset al.11 have evaluated the structural parametersfor trans-glyoxal. These parameters are in excellent agree-ment with electron diffraction results.36 In general, these ex-perimental geometries are in good agreement with theoreticalresults.24,26,28,33–35,38–43The product of the principal mo-ments of inertia for the planar structure oftrans-glyoxal ofC2h symmetry was calculated here using the rotational con-stants determined from a high-resolution Fourier-transformstudy of trans-glyoxal.15 Structural parameters oftrans-glyoxal given above are those obtained from an electron dif-fraction investigation.36 These parameters reproduce thespectroscopic moments of inertia with in an accuracy of0.2%–0.3%.
Rotational constants for the ground state ofcis-glyoxalwere obtained from rotational analysis of the 0–0 band6,8 andby microwave spectroscopy.7,10,12,17,18The product of theprincipal moments of inertia for the planar structure ofcis-glyoxal of C2n symmetry was calculated in this work usingthe rotational constants determined from microwavestudies.17,18 Sets of possible structural parameters ofcis-glyoxal were evaluated using the rotational constants for itsisotopomers combined with assumptions of the values ofsome parameters.7,8,10,28,44The geometry ofcis-glyoxal wasalso calculated byab initio22,24,26–29,31–33,35,38,39,41,42and mo-lecular mechanics43 methods. Structural parameters ofcis-glyoxal shown above were proposed by Tyulinet al.44 fromanalysis of microwave data.17
Vibrational spectra of glyoxal were studied in the gasphase4–8,10,13,15,16,45–55 and with matrix isolationtechniques.56–58 The experimental assignments have beenconfirmed by normal coordinate analyses44,59–64and theoret-ical calculations.26,28,29,31,34,35,40,43,65–70The adopted valuesfor vibrational frequencies oftrans-glyoxal were taken fromthe investigation of dispersed fluorescence spectra53 (n1
2n5 ,n8), high-resolution infrared spectra48
(n6 ,n7 ,n11,n12), a rotational fine structure of the C–H
stretching band5 (n9) and a high-resolution infrared Fourier-transform study15 (n10). The uncertainties in these values arewithin 0.5 cm21. The adopted values ofn12n7 andn10 fun-damental frequencies ofcis-glyoxal are those observed fromgas and Ar-matrix spectra.13,18,55,58For unobserved frequen-cies (n8 ,n9 ,n11,n12), the values were selected on the basisof ab initio calculations;28,31,35,68and their uncertainties areestimated to be 25–50 cm21.
The torsional potential function for glyoxal has been in-vestigated experimentally3,6,7,9,13,16,18,71 andtheoretically19–34,70,72 by many authors. An early infraredstudy3 suggested a very hightrans-cisrotation barrier (Vrot)of 4810 cm21 based on a torsional frequency of 128 cm21.Currie and Ramsay6 provided the first estimate forcis-transenthalpy difference,DH5(11256100) cm21, from the tem-perature dependence ofcis andtransabsorption bands in thevisible spectrum. Duriget al.9 obtained the torsional poten-tial function for glyoxal that fits the infrared data of thetransconformer and the microwave intensity data of thecis con-former and yields theDH5(11806150) cm21 with a barrierheightVrot51770 cm21. The energy difference between thecis and trans conformers has been revised upwards twice byButz et al., first to (13506200) cm21 derived from a spec-troscopic temperature study13 and then to (16886100) cm21
by fitting spectroscopic data to a torsional potential.16 Thepotential function obtained by Butzet al.16 has a barrier totrans-cis rotation of 2077 cm21. Recently Hu¨bner et al.18
have determined thecis-trans enthalpy difference,DH5(1555648) cm21, from absorption intensities of glyoxalby microwave spectroscopy. This value is intermediate be-tween the values reported by Butzet al.13,16 Based on thisvalue forDH, Hubneret al.18 have recalculated the potentialcurve for internal rotation in glyoxal (Vrot52003 cm21). Nu-merousab initio calculations yield different results forDHdepending on the basis sets and levels of calculation~1050,20
1700–2200,23 ;2000,22,24,25,28,30and 2422 cm21!.70 Due tothis wide range they are not of help in deciding among theavailable experimental data.
The torsional potential function determined by Hu¨bneret al.18 is accepted in this work in order to account for theinternal rotation in glyoxal. The Fourier expansion coeffi-cients for the internal rotation constantB were adopted to bethe same as those used by Duriget al.9 and later by otherauthors.16,18The values of the reduced moment of inertia,I r ,were calculated from accepted structural parameters~seeabove!.
Experimentally observed absorption spectra of glyoxalhave been identified with transitions to the excited elec-tronic states a 3Au (T0519 199 cm21) and A 1Au (T0
521 973 cm21).45,73,74 These assignments agree with otherexperimental75–79 and theoretical35,80,81studies. Dykstra andSchaefer82 have predicted two low-lying~;15 000 cm21!unobserved triplet states fromab initio calculation. Becauseof high energies of excited electronic states of glyoxal, theyare not considered in this work. These electronic stateswould only make an appreciable contribution to the thermo-
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J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
dynamic functions at temperatures above 3000 K.The uncertainties in the calculated thermodynamic func-
tions ~Table 5! are estimated to be~0.5–3.0! J K21 mol21 forCp°(T) and ~1.0–3.0! J K21 mol21 for S°(T).
The thermodynamic functions of glyoxal as an equilibriummixture of trans and cis conformers were calculated byCompton.83 The discrepancies betweenCp°(T) and S°(T)values calculated in this work and in Compton83 increasewith temperature and reach 3.1 and 2.2 J K21 mol21, respec-tively, at 1000 K. These discrepancies are due to different
molecular constants used in the calculations and the nonin-clusion of internal rotation in glyoxal by Compton.83 Valuesof H°(T)2H°(0) given by Compton appear to be in error.Hollensteinet al.84 derived the thermodynamic functions ofglyoxal using the semiclassical approximation for the sum-over-states calculation for nonrigid molecules. The differ-ence between theirCp°(T) andS°(T) values and those cal-culated in this work range from 0.1 to 8.8 J K21 mol21
depending on the level of approximation used. The discrep-ancies with the results of statistical calculations by Natarajan
TABLE 5. Ideal gas thermodynamic properties of glyoxal C2H2O2(g) at the standard state pressure,p°50.1 MPa~Tr5298.15 K)
et al.85 amount to~50–60! J K21 mol21 and cannot be due todifferences in the molecular constants used.
6.3. References
1R. A. Fletcher and G. Pilcher, Trans. Faraday Soc.66, 794 ~1970!.2L. A. Curtiss, K. Raghavachari, P. C. Redfern, and J. A. Pople, J. Chem.Phys.106, 1063~1997!.
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4F. W. Birss, J. M. Brown, A. R. H. Cole, A. Lofthus, S. L. N. G. Krish-namachari, G. A. Osborne, J. Paldus, D. A. Ramsay, and L. Watmann,Can J. Phys.48, 1230~1970!.
5A. R. H. Cole and G. A. Osborne, J. Mol. Spectrosc.36, 376 ~1970!.6G. N. Currie and D. A. Ramsay, Can. J. Phys.49, 317 ~1971!.7J. R. Durig, C. C. Tong, and Y. S. Li, J. Chem. Phys.57, 4425~1972!.8D. A. Ramsay and C. Zauli, Acta Phys. Acad. Sci. Hung.35, 79 ~1974!.9J. R. Durig, W. E. Bucy, and A. R. H. Cole, Can. J. Phys.53, 1832~1975!.
10A. R. H. Cole, Y. S. Li, and J. R. Durig, J. Mol. Spectrosc.61, 346~1976!.11F. W. Birss, D. B. Braund, A. R. H. Cole, R. Engleman, Jr., A. A. Green,
S. M. Japar, R. Nanes, B. J. Orr, D. A. Ramsay, and J. Szyszka, Can. J.Phys.55, 390 ~1977!.
12A. Kh. Mamleev, R. G. Latypova, L. N. Gunderova, V. I. Tyulin, and N.M. Pozdeev, Zh. Strukt. Khim.21, 46 ~1980!.
13K. W. Butz, J. R. Johnson, D. J. Krajnovich, and C. S. Parmenter, J.Chem. Phys.86, 5923~1987!.
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Johns, Can. J. Phys.65, 1636~1987!.16K. W. Butz, D. J. Krajnovich, and C. S. Parmenter, J. Chem. Phys.93,
1557 ~1990!.17N. M. Pozdeev, A. H. Mamleev, L. N. Gunderova, R. V. Galeev, G. R.
Garipova, and V. I. Tyulin, Zh. Strukt. Khim.36, 418 ~1995!.18H. Hubner, A. Leeser, A. Burkert, D. A. Ramsay, and W. Hu¨ttner, J. Mol.
Spectrosc.184, 221 ~1997!.19U. Pincelli, B. Cadioli, and D. J. David, J. Mol. Struct.9, 173 ~1971!.20T. K. Ha, J. Mol. Struct.12, 171 ~1972!.21K. R. Sundberg and L. M. Cheung, Chem. Phys. Lett.29, 93 ~1974!.22C. E. Dykstra and H. F. Shaefer III, J. Am. Chem. Soc.97, 7210~1975!.23P. N. Skancke and S. Saebø, J. Mol. Struct.28, 279 ~1975!.24Y. Osamura and H. F. Shaefer III, J. Chem. Phys.74, 4576~1981!.25G. R. De Mare, J. Mol. Struct: THEOCHEM107, 127 ~1984!.26T. J. Kakumoto, Sci. Hiroshima Univ. A51, 69 ~1987!.27S. Saebo”, Chem. Phys.113, 383 ~1987!.28C. W. Bock, Y. N. Panchenko, and S. V. Krasnoshchiokov, Chem. Phys.
125, 63 ~1988!.29G. E. Scuseria and H. F. Schaefer III, J. Am. Chem. Soc.111, 7761
~1989!.30C. W. Bock and A. Toro-Labbe, J. Mol. Struct: THEOCHEM232, 239
~1991!.31G. R. De Mare, J. Mol. Struct: THEOCHEM253, 199 ~1992!.32G. R. De Mare, Yu. N. Panchenko, and A. V. Abramenkov, J. Phys.
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Struct: THEOCHEM393, 39 ~1997!.35J. F. Stanton and J. Gauss, Spectrochim. Acta A53, 1153~1997!.36K. Kuchitsu, T. Fukuyama, and Y. Morino, J. Mol. Struct.1, 463 ~1968!.37J. Paldus and D. A. Ramsay, Can. J. Phys.45, 1389~1967!.38C. W. Bock, P. George, C. J. Mains, and M. Trachtman, J. Mol. Struct.49,
211 ~1978!.39P. George, C. W. Bock, and M. Trachtman, J. Mol. Struct.69, 183~1980!.40P. Pulay, G. Fogarasi, G. Pongor, J. E. Boggs, and A. Vargha, J. Am.
Chem. Soc.105, 7037~1983!.41C. Van Alsenoy, V. J. Klimkowski, and L. Scha¨fer, J. Mol. Struct:
THEOCHEM 109, 321 ~1984!.
42N. L. Allinger, L. Schafer, K. Siam, V. J. Klimkowski, and C. Van Alse-noy, J. Comput. Chem.6, 331 ~1985!.
43N. L. Allinger and Y. Fan, J. Comput. Chem.15, 251 ~1994!.44V. I. Tyulin, G. M. Kuramshina, Y. A. Pentin, and L. H. Ho, Zh. Strukt.
Khim. 38, 287 ~1997!.45J. C. D. Brand, Trans. Faraday Soc.50, 431 ~1954!.46R. K. Harris, Spectrochim. Acta20, 1129~1964!.47W. Holzer and D. A. Ramsay, Can. J. Phys.48, 1759~1970!.48A. R. H. Cole and G. A. Osborne, Spectrochim. Acta A27, 2461~1971!.49R. Y. Dong and D. A. Ramsay, Can. J. Phys.51, 1491~1973!.50A. B. Duval, D. A. King, R. Haines, N. R. Isenor, and B. J. Orr, J. Raman
Spectrosc.17, 177 ~1986!.51G. A. Bickel and K. K. Innes, J. Chem. Phys.86, 1752~1987!.52D. Frye, L. Dai, and H.-L. Lapierre, J. Chem. Phys.89, 2609~1988!.53E. Pebay Peyroula, A. Delon, and R. Jost, J. Mol. Spectrosc.132, 123
~1988!.54W. G. Wickun and K. K. Innes, J. Mol. Spectrosc.127, 277 ~1988!.55R. Y. Dong, R. Nanes, and D. A. Ramsay, Can. J. Chem.71, 1595~1993!.56M. Diem, B. G. MacDonald, and E. K. C. Lee, J. Phys. Chem.85, 2227
~1981!.57L. J. Van IJzendoorn, L. J. Allamandola, F. Baas, S. Ko¨rnig, and J. M.
Greenberg, J. Chem. Phys.85, 1812~1986!.58A. Engdahl and B. Nelander, Chem. Phys. Lett.148, 264 ~1988!.59T. Fukuyama, K. Kuchitsu, and Y. Morino, Bull. Chem. Soc. Jpn.41,
3019 ~1968!.60C. Cossart-Magos, Spectrochim. Acta A34, 415 ~1978!.61H. J. Oelichmann, D. Bougeard, and B. Schrader, J. Mol. Struct.77, 149
~1981!.62L. O. Pietila, K. Palmo, and B. Mannfors, J. Mol. Spectrosc.112, 104
~1985!.63L. O. Pietila, K. Palmo, and B. Mannfors, J. Mol. Spectrosc.116, 1
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~1979!.68Y. N. Panchenko, G. R. De Mare, and V. I. Pupyshev, J. Phys. Chem.99,
17544~1995!.69X. Zhou, C. J. M. Wheeless, and R. Liu, Vib. Spectrosc.12, 53 ~1996!.70M. L. Senent, J. Mol. Struct.406, 51 ~1997!.71H. H. Le and V. I. Tyulin, Zh. Strukt. Khim.16, 63 ~1975!.72E. L. Coitino and J. Tomasi, Chem. Phys.204, 391 ~1996!.73G. W. King, J. Chem. Soc. 5054~1957!.74D. A. Ramsay, M. Verloet, F. Vanhorenbeke, M. Godefroid, and M. Her-
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Phys. Lett.8, 232 ~1971!.77L. G. Anderson, C. S. Parmenter, and H. M. Poland, Chem. Phys.1, 401
~1973!.78J. Kelder, H. Cerfontain, J. K. Eweg, and R. P. H. Rettschnick, Chem.
Phys. Lett.26, 491 ~1974!.79J. M. Leclercq, C. Mijoule, and F. Yvan, J. Chem. Phys.64, 1464~1976!.80C. E. Dykstra, R. R. Lucchese, and H. F. Schaefer III, J. Chem. Phys.67,
2422 ~1977!.81W. B. Mueller, J. F. Harrison, and P. J. Wagner, J. Am. Chem. Soc.100,
33 ~1978!.82C. E. Dykstra and H. F. Schaefer III, J. Am. Chem. Soc.98, 401 ~1976!.83D. A. C. Compton, J. Chem. Soc., Perkin Trans. 2, 1307~1977!.84H. Hollenstein, A. Bauder, and H. H. Gu¨nthard, Chem. Phys.47, 269
~1980!.85A. Natarajan, P. Kolandaivelu, and A. Savarianandam, J. Indian Chem.
r (CvO)51.1960.02 År (C—C)51.4760.02 År (wN)51.1660.02 Å/OvC—C512863°/C—CwN517065°
Product of moments of inertia:I AI BI C51833102117 g3 cm6.
7.1. Enthalpy of Formation
No experimental data are available for enthalpy of forma-tion of the cyanooxomethyl radical. The value accepted inthis work was estimated by Francisco and Liu1 by using theisodesmic reaction approach with the following reaction:
OCCN1HCN→C2N21HCO.
The relationship between the enthalpy of formation ofOCCN and the enthalpy change of the above reaction is
D fH°~OCCN!5D fH°~C2N2!1D fH°~HCO!
2D fH°~HCN!2D rH°.
Based on known experimental enthalpies of formation ofHCN, C2N2, HCO, and theD rH° value predicted byab ini-tio calculations, Francisco and Liu1 have estimated the en-thalpy of formation for OC˙ CN to be 207.5–210.0 kJ mol21.
7.2. Heat Capacity and Entropy
There are no experimental data on structure and vibra-tional spectra of OC˙ CN. According to ab initiocalculations,1,2 a bent structure ofCs symmetry is adopted inthis work for OCCN in the ground electronic stateX 2A8.The product of the principal moments of inertia was calcu-lated using the structural parameters shown above. These
values are based on the results ofab initio calculations1,2 andcomparison with structural parameters of CO~CN!2, COX2,and XCO (X5F, Cl) molecules.
Vibrational frequencies of OC˙ CN were calculated in thiswork using the following force constants:
f CvO511.413 mdyn/Å, f C—CwN50.110 mdyn Å,
f C—C57.225 mdyn/Å, f CC,CO50.513 mdyn/Å,
f CwN513.674 mdyn/Å, f CC,CN521.543 mdyn/Å,
f C—CvO50.750 mdyn Å, f CC,CCO50.585 mdyn.
These constants were transferred from the CO~CN!2 mol-ecule except forf C—C5O and f C—C[N whose values werereduced by comparison with the bending force constants inCOX2 and XCO (X5F, Cl, Br). Normal coordinate analysisfor CO~CN!2 was carried using the vibrational assignment ofMiller et al.3 The uncertainties in the calculated frequenciesof OCCN can reach 50 cm21. These frequencies agree over-all with those resulting from theab initio calculation.1
The first excited electronic stateA 2A9 of OCCN was pre-dicted at an energy of;15 500 cm21 by an ab initiocalculation1 and was included in the calculations in thiswork. Structural parameters and vibrational frequencies forthe A 2A9 state were accepted as identical to those of theground state.
496496 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
The uncertainties in the calculated thermodynamic func-tions ~Table 6! are estimated to be~1.5–2.0! J K21 mol21 forCp°(T) and ~1.5–3.0! J K21 mol21 for S°(T).
Ideal gas thermodynamic properties of the cyanooxom-ethyl radical have not been reported previously.
7.3. References
1J. S. Francisco and R. Liu, J. Chem. Phys.107, 3840~1997!.2A. L. Cooksy, J. Am. Chem. Soc.117, 1098~1995!.3F. A. Miller, B. M. Harney, and J. Tyrrell, Spectrochim. Acta A27, 1003~1971!.
TABLE 6. Ideal gas thermodynamic properties of the cyanooxomethyl radical C2NO~g! at the standard state pressure,p°50.1 MPa (Tr5298.15 K)
aInstead of torsional moden10;90 cm21, the contributions due to theinternal rotation about C–C bond were calculated from the potentialV(w)5 1
2V1(12cosw), where w is the torsional angle andV1
5700 cm21.
COOH top: Reduced moment of inertia,I r53.6454310239 g cm2, Symmetry number,sm51
Geometryr ~C—C!51.54860.004 År ~CvO!51.20860.001 År ~C—O!51.33960.002 År ~O—H!51.05660.014 Å/C—CvO5123.160.9°/OvC—O5125.060.2°/C—O—H5104.462.3°
Product of moments of inertia:I AI BI C511 9503102117 g3 cm6.
8.1. Enthalpy of Formation
Wilhoit and Shiao1 have measured the enthalpy of com-bustion of solid oxalic acid in a rotating platinum bomb calo-rimeter and have calculated D fH°~C2H2O4,cr,298.15 K!52~829.961.0) kJ mol21. The enthalpy of for-mation of gaseous oxalic acid is calculated from this valueby adding the enthalpy of sublimation,DsubH°598.1kJ mol21, obtained from vapor pressure measurements.2
8.2. Heat Capacity and Entropy
Nahlovskaet al.3 carried out an electron diffraction and anIR study of oxalic acid indicating that the structure was in aplanar trans conformation ~C2h symmetry! in which the
hydrogen atom of one COOH group participated in intramo-lecular hydrogen bonding with the carbonyl oxygen of theother COOH group~‘‘hydrogen bonded’’trans conformer!.Infrared matrix-isolation spectra of oxalic acid4 were inter-preted in terms of the same model and the tentative conclu-sion was made that a second conformer of oxalic acid existsin the vapor phase. This conformer was suggested to be atrans form ~C2h symmetry! with the hydrogen atom of eachCOOH group oriented towards the carbonyl oxygen of thesame COOH group~‘‘free’’ trans form!. Oxalic acid wasdetermined to be in itstrans conformation from x-ray crys-tallographic studies5 and no other conformers were observed.Studies of oxalic acid in solution6 favored almost free rota-
498498 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
tion, which would include a range of possible conformations.Ab initio studies of oxalic acid7–9 have obtained a moststable hydrogen bondedtrans planar structure in agreementwith the results of an electron diffraction investigation.3 Thehydrogen bonded or freetrans form was found to be lowestenergy depending on the basis set used in theab initiocalculations.10 The freetrans conformer was reported to bemost stable by an earlierab initio study.11
The hydrogen bondedtrans form ~C2h symmetry! is ac-cepted for oxalic acid in this work. Its product of principalmoments of inertia was calculated using the structural pa-rameters determined from the electron diffraction study.3
Following the results of a theoretical calculation by Tyrrell,9
it was assumed that there is a slight energy preference forthis conformer and only a small barrier of about 2 kcal mol21
~700 cm21! separating it from other stable conformers. Thesimple approximate potential,
V~w!5 12V1~12cosw!,
wherew is the OC—CO torsional angle, was used here forthe calculation of internal rotational contributions to the ther-modynamic functions of oxalic acid. The value of the re-duced moment of inertia for the COOH top was derived fromthe molecular constants shown above.
There are several studies of the vibrational spectra of thefree C2H2O4 molecule3,4,12–14but some fundamentals are stillunobserved. Stace and Oralratmanee14 have reported the in-frared vapor phase measurements and the first vapor phaseRaman spectra. They have proposed a new vibrational fre-quencies assignment based on their experimental results aswell as calculated in-plane frequencies using an Urey–Bradley force field derived from formic and acetic acid. Red-ington and Redington4 have investigated the infrared spectraof oxalic acid vapor and the infrared spectra of matrix-isolated C2H2O4, C2HDO4, and C2D2O4 and have carried outa normal coordinate analysis using a general valence forcefield for the in-plane infrared-active modes. None of theabove studies, however, gives a complete vibrational assign-ment for oxalic acid. De Villepin and Novak15 have devel-oped a general valence force field for both infrared and Ra-man frequencies using the relatively small number ofexperimentally observed fundamentals. Their force field re-produces the experimental vibrational spectra of oxalic andis comparable with force fields already known for other car-boxylic acids. The fundamental frequenciesn22n5 and n7
adopted here were observed in the Raman spectra of gaseousoxalic acid.14 The 405 cm21 mode was subsequently reas-signed ton7 .4 The values ofn8 , n9 , n132n16, andn18 arethose determined from gas-phase infrared spectra.4 The valuefor n17 was obtained from spectra of neon matrix-isolatedoxalic acid.4 The uncertainties in these experimental frequen-cies are in the range of 5–10 cm21.
Redington and Redington4 have suggested tentative valuesfor n6(Ag)5538 cm21, n11(Bg)5590 cm21, and n12(Bg)5512 cm21 fundamentals using possible combination bands.
The adopted values of these frequencies were taken fromnormal coordinate calculations.15 Calculations for the otherfrequencies are in good agreement with experimental results.The value of the symmetric O—H stretching frequencyn1
was accepted to be the same as the value of antisymmetricO—H stretching (n13) and it coincides with the calculatedvalue.15 The uncertainties in these frequencies are estimatedto be 25–50 cm21.
Evidently due to its weak intensity, the C—C torsionmode n10(Au) was not observed in a vapor phase spectrasearch that extended down to 35 cm21.4 Ab initiocalculations8,10 have suggested the value of 160 cm21 for thetorsional mode, however, it should be noted that all othercalculated values are much greater than those from experi-ment. Cyvin and Alfheim16 have calculatedn10590 cm21
using force constants transferred from formic and acetic ac-ids. The value of 110 cm21 was obtained from other normalcoordinate calculation.15 The corresponding torsional modefor oxalyl fluoride ~F—CO—CO—F! was observed in thegas phase at 54 cm21 and in the solid phase at 94 cm21.17
From the ratio of n tors~C2F2O2, solid!/ntors~C2F2O2, gas)51.74 and the value of 138 cm21 for the torsional mode ofsolid oxalic acid,15,18the value of;80 cm21 for the torsionalmode of gaseous oxalic acid is expected.
The uncertainties in the calculated thermodynamic func-tions ~Table 7! may be as much as~5–7! J K21 mol21 forCp°(T) and~5–10! J K21 mol21 for S°(T). These uncertain-ties arise from the uncertainties in the adopted values of thevibrational frequencies and the simple and approximatemodel for internal rotation.
Ideal gas thermodynamic properties of oxalic acidhave not been reported previously.
8.3. References
1R. C. Wilhoit and D. Shiao, J. Chem. Eng. Data9, 595 ~1964!.2R. S. Bradley and S. Cotson, J. Chem. Soc. 1684~1953!.3Z. Nahlovska, B. Nahlovsky, and T. G. Strand, Acta Chem. Scand.24,2617 ~1970!.
4R. L. Redington and T. E. Redington, J. Mol. Struct.48, 165 ~1978!.5J. L. Derissen and P. H. Smit, Acta Crystallogr. Sect. B: Struct. Crystollgr.Cryst. Chem.30, 2240~1974!.
6T. A. Shippey, J. Mol. Struct.65, 71 ~1980!.7C. Van Alsenoy, V. J. Klimkowski, and L. Scha¨fer, J. Mol. Struct:THEOCHEM 109, 321 ~1984!.
8T. Kakumoto, J. Sci. Hiroshima Univ. A51, 69 ~1987!.9J. Tyrrell, J. Mol. Struct: THEOCHEM258, 389 ~1992!.
10T. Kakumoto, K. Saito, and A. Imamura, J. Phys. Chem.91, 2366~1987!.11D. Ajo, G. Condorelli, I. Fragala, and G. Granozzi, J. Mol. Struct.37, 160
~1977!.12M. Pava Bruce and F. E. Stafford, J. Phys. Chem.72, 4628~1968!.13L. Bardet, G. Fleury, and V. Tabacik, C. R. Acad. Sci. B270, 1277
~1970!.14B. C. Stace and C. Oralratmanee, J. Mol. Struct.18, 339 ~1973!.15J. De Villepin, A. Novak, and D. Bougeard, Chem. Phys.73, 291 ~1982!.16S. J. Cyvin and I. Alfheim, Acta Chem. Scand.24, 2648~1970!.17J. R. Durig, S. C. Brown, and S. E. Hannum, J. Chem. Phys.54, 4428
~1971!.18J. De Villepin, A. Novak, and F. Romain, Spectrochim. Acta A34, 1009
~1978!.
499499NIST-JANAF THERMOCHEMICAL TABLES
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
9. Methyl Hydroperoxide, CH 3AOAOAH
Methyl hydroperoxide (CH4O2) Ideal gas Mr548.0414D fH°(0 K)52126.265.0 kJ mol21
S°(298.15 K)5276.563.0 J K21 mol21 D fH°(298.15 K)52139.065.0 kJ mol21
Molecular constantsPoint group:C1 Symmetry number:s51 Number of optical isomers:n52Ground electronic state:X 1A Energy:eX50 cm21 Quantum weight:gX51
aInstead of torsional moden145240 cm21, the contributions due to theinternal rotation of CH3 group around the C—O bond were calculatedfrom the potentialV(w)5 1
2V3(12cos3w), wherew is the H—C—O—Otorsional angle andV351120 cm21.bInstead of torsional moden155149 cm21, the contributions due to theinternal rotation of OH group around the O-O bond were calculated fromthe potential:V(w)5V01V1 cosw1V2 cos2w1V3 cos3w, wherew is theC—O—O—H torsional angle,V05780.7,V151111.1,V25555.6, andV3552.6 ~in cm21!.
CH3 top: Reduced moment of inertia,I r50.4282310239 g cm2, Symmetry number,sm53.
OH top: Reduced moment of inertia,I r50.138310239 g cm2, Symmetry number,sm51.
Geometryr ~C—H!51.09060.010 År ~O—H!50.97060.005 Å/C—O—O5105.360.5 Å/O—O—H5100.062.0°/H—C—O5109.564.0°w~C—O—O—H!512065°r ~C—O!51.42060.005 År ~O—O!51.46060.010 Å
Rotational constants in cm21:A051.434 544 B050.350 826 C050.301 985.
Product of moments of inertia:I AI BI C5144.33102117 g3 cm6.
9.1. Enthalpy of Formation
Experimental data on enthalpy of formation are not avail-able for methyl hydroperoxide. Values ofD fH°~CH3OOH,g,298.15 K! between 2122 and 2138kJ mol21 were estimated from semiempirical,1–3 molecularmechanics,4–6 ab initio,7 and group additivity8–10 calcula-tions. Lay et al.11 have estimatedD fH° ~298.15 K! to be(139.765.0) kJ mol21 using the experimentally determinedvalue ofD fH°(CH3OO) with an average bond energy for theO–H bond in ROOH compounds. Based on the experimentalvalues ofD fH°(CH3O), D fH°(OH),12 and the bond energyof the O–O bond in CH3OOH,13 the value of2134.3 kJmol21 may be obtained for the enthalpy of formation of me-thyl hydroperoxide. Benassiet al.5 proposed D fH°(298.15 K)52138.1 kJ mol21 by employing theoretical andempirical approaches. Similar values ofD fH° are predictedby the method of group equations from
D fH°~CH3OOH!
5D fH°~CH3OOCH3!1D fH°~CH3OH!
2D fH°~CH3OCH3!
5~2125.5!1~2201.5!2~2184.1!
52142.9 kJ mol21,
D fH°~CH3OOH!
5D fH°~CH3CH2OOH!1D fH°~CH3OH!
2D fH°~CH3CH2OH!
5~2173.6!1~2201.5!2~2235.2!
52139.9 kJ mol21,
~the D fH° values were taken from Pedley14 ~CH3OH,CH3OCH3, and CH3CH2OH!, Bakeret al.15 (CH3OOCH3),and Layet al.11 (CH3CH2OOH). The average of these esti-
501501NIST-JANAF THERMOCHEMICAL TABLES
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
mates,213965.0 kJ mol21, is accepted in this work for theenthalpy of formation of methyl hydroperoxide at 298.15 K.
9.2. Heat Capacity and Entropy
The microwave spectrum of methyl hydroperoxide,CH3OOH, has been investigated by Tyblewskiet al.16 How-ever, the assignment of the spectrum was complicated be-cause of the widespread effects of the internal rotationaround the O—O bond. The experimental results providedefinitive evidence that the minimum of the potential energyrelative to internal rotation around the O—O bond corre-sponds to askewconformation. The adjustment to the ob-served data resulted in a smalltrans barrier of 172.5 cm21.This barrier separates two equivalent potential minima asso-ciated with two enantiomericskew forms. From a prelimi-nary interpretation of microwave data, Tyblewskiet al.17 re-ported almost all the structural parameters of the CH3OOHmolecule. In a more detailed study, Tyblewskiet al.16 gaveonly one parameter adjusted to the observed data,/C—C—O5105.3°. All other structural parameters wereadopted by those authors fromab initio calculations. Confor-mational properties of methyl hydroperoxide have been in-vestigated theoretically.1,2,4–6,11,16,18–22Ab initio5,16,19–22andmolecular mechanics4,6 calculations provide an equilibriummolecular structure andtransbarrier in close agreement withthe conclusions of experimental study of Tyblewskiet al.16
The product of the principal moments of inertia of methylhydroperoxide was calculated in this work using the rota-tional constants determined from a microwave study.16
Structural parameters for theskew C1 symmetry conforma-tion given above are based on the experimental16 andtheoretical4–6,16,19–22data for CH3OOH and from comparisonwith the structural parameters of CH3OOCH3.
23 These pa-rameters give values for the rotational constants which differby only 0.4%–0.6% from the observed values.
Methyl hydroperoxide contains OH and CH3 groups,which rotate around O—O and C—O bonds. Contributionsto the thermodynamic functions from these hindered rotorswere evaluated in this work based on available data on rota-tional barriers in CH3OOH. The value ofV351120 cm21
was accepted for the barrier to internal rotation of the methylgroup around the C—O bond. This value was found from themicrowave study16 and agrees closely with values obtainedfrom ab initio calculations.4,16 The double-minimum poten-tial energy function,
V~w!5V01V1 cosw1V2 cos 2w1V3 cos 3w,
was used in this work for the O—O internal rotation. Thisfunction was chosen earlier for the hindered rotation poten-tial function in hydrogen peroxide.24 The expansion coeffi-cientsV0 , V1 , V2 , andV3 can be expressed in terms of thetrans barrier heightVtrans , the cis barrier heightVcis , andthe COOH dihedral anglewe corresponding to a minimum ofthe potential function.24 The values ofV0 , V1 , V2 , andV3
were calculated in this work assumingVtrans5172.5 cm21,Vcis52500 cm21, and we5120°. The value of Vtrans
5172.5 cm21(/C—O—O—H5180°) was taken from themicrowave study.16 It should be noted that substantiallylower values ofVtrans from 80 to 126 cm21 were predictedby ab initio5,16,19,20and molecular mechanics6 calculations,whereas highVtrans values of 240–590 cm21 were foundfrom other molecular mechanics studies.4,5 No experimentaldata for theVcis rotational barrier have been published. Itsvalue accepted in this work is based on theoreticalresults4–6,16,25which agree closely with each other. The equi-librium COOH dihedral angle,we5120°, was estimated inthis work ~see above!. The values of the reduced moments ofinertia for CH3 and OH tops were calculated from structuralparameters given above.
Experimental data on the vibrational spectra of methyl hy-droperoxide are unknown. Vibrational frequencies ofCH3OOH were predicted fromab initio calculations.16,22 Inthis work, fundamental frequencies of methyl hydroperoxidewere estimated by normal coordinate calculations using forceconstants transferred from the CH3OOCH3 and H2O2 mol-ecules:f O—O 5.000 f O—O—H 0.940 f C—H,H—C—O 20.056f C—O 5.529 f tors~C—O! 0.094 f C—H,H—C—H 0.090f C—H 4.692 f tors~O—O! 0.011 f C—O,H—C—O 0.240f O—H 7.173 f C—H,C—H 0.041 f C—O,C—O—O 1.735f C—O—O 1.512 f C—H,C—O 0.250 f O—O,C—O—O 0.617f H—C—O 0.820 f C—O,O—O 0.267 f O—O,O—O—H 0.919f H—C—H 0.516 f O—O,O—H 20.317 f O—H,O—O—H 0.925
~stretching and stretch-stretch interaction constants are inunits of mdyn/Å; bend and torsion constants are in units ofmdyn Å; stretch-bend interaction constants are in units ofmdyn!. The valence force fields for CH3OOCH3 and H2O2
were obtained from normal coordinate calculations usingknown vibrational assignments.6,26 Comparison of our fre-quencies with those obtained inab initio calculations16,22
shows satisfactory agreement taking into account the factthat theab initio frequencies are unscaled and the anharmo-nicity contributions are neglected.
The uncertainties in the calculated thermodynamic func-tions ~Table 8! may reach~2–4! J K21 mol21 for Cp°(T) and~3–5! J K21 mol21 for S°(T). They are caused by the uncer-tainties in the adopted vibrational frequencies and the ap-proximate model used for internal rotation.
Ideal gas thermodynamic properties of methyl hydroper-oxide have not been reported previously.
9.3. References
1C. Glidewell, J. Mol. Struct.67, 35 ~1980!.2V. N. Kokorev, N. N. Vyshinskii, V. P. Maslennikov, I. A. Abronin, G.M. Zhidomirov, and Yu. A. Aleksandrov, Zh. Strukt. Khim.22, 9 ~1981!.
3M. Jonsson, J. Phys. Chem.100, 6814~1996!.4L. Carballeira, R. A. Mosquera, and M. A. Rios, J. Comput. Chem.9, 851~1988!.
5R. Benassi, U. Folli, S. Sbardellati, and F. Taddei, J. Comput. Chem.14,379 ~1993!.
6K. Chen and N. L. Allinger, J. Comput. Chem.14, 755 ~1993!.7T. P. W. Jungkamp and J. H. Seinfeld, Chem. Phys. Lett.257, 15 ~1996!.
502502 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
8S. W. Benson, J. Chem. Phys.40, 1007~1964!.9S. W. Benson, J. Am. Chem. Soc.86, 3922~1964!.
10P. S. Nangia and S. W. Benson, J. Phys. Chem.83, 1138~1979!.11T. H. Lay, L. N. Krasnoperov, C. A. Venanzi, J. W. Bozzelli, and N. V.
Shokhirev, J. Phys. Chem.100, 8240~1996!.12L. V. Gurvich, I. V. Veyts, and C. B. Alcock,Thermodynamic Properties
of Individual Substances, 4th ed.~Hemisphere, New York, 1991!, Vol. 2.13R. D. Bach, P. Y. Ayala, and H. B. Schlegel, J. Am. Chem. Soc118,
12758~1996!.14J. B. Pedley,Thermochemical Data and Structures of Organic Com-
pounds~Thermodynamics Research Center, College Station, TX, 1994!,Vol. I.
15G. Baker, J. H. Littlefair, R. Shaw, and J. C. J. Thynne, J. Chem. Soc.6970 ~1965!.
16M. Tyblewski, T. K. Ha, R. Meyer, A. Bauder, and C. E. Blom, J. Chem.Phys.97, 6168~1992!.
17M. Tyblewski, R. Meyer, and A. Bauder, 8th Colloquium on High Reso-lution Molecular Spectroscopy, Tours, France, 1983.
18K. Ohkubo, T. Fujita, and H. Sato, J. Mol. Struct.36, 101 ~1977!.19R. A. Bair and W. A. Goddard III, J. Am. Chem. Soc.104, 2719~1982!.20D. Christen, H. G. Mack, and H. Oberhammer, Tetrahedron44, 7363
~1988!.21J. Koller, M. Hodoscek, and B. Plesnicar, J. Am. Chem. Soc.112, 2124
~1990!.22R. Benassi and F. Taddei, Tetrahedron50, 4795~1994!.23B. Haas and H. Oberhammer, J. Am. Chem. Soc.106, 6146~1984!.24R. H. Hunt, R. A. Leacock, C. W. Peters, and K. T. Hecht, J. Chem. Phys.
42, 1931~1965!.25L. Radom, W. J. Hehre, and J. A. Pople, J. Am. Chem. Soc.94, 2371
~1972!.26P. G. Giguere and T. K. K. Srinivasan, J. Raman Spectrosc.2, 125~1974!.
TABLE 8. Ideal gas thermodynamic properties of methyl hydroperoxide CH4O2~g! at the standard state pressure,p°50.1 MPa (Tr5298.15 K)
aInstead of torsional modesn125218 cm21 and n245231 cm21, thecontributions due to the internal rotation of CH3 groups around C—Obonds were calculated from the potentialV(w)5 1
2V3(12cos 3w), wherew is the H—C—O—O torsional angle andV35900 cm21.bInstead of torsional moden13573 cm21, the contributions due to theinternal rotation of OCH3 group around O—O bond were calculatedfrom the potentialV(w)5V01V1 cosw1V2 cos 2w1V3 cos 3w, wherewis the C—O—O—C torsional angle,V051341.3, V152081.0, V2
51052.2, andV35225.5~in cm21!.
CH3 top: Reduced moment of inertia,I r50.4910310239 g cm2, Symmetry number,sm53.
OCH3 top: Reduced moment of inertia,I r51.5928310239 g cm2, Symmetry number,sm51.
Geometryr (C—O)51.42060.007 År (O—O)51.45760.012 År (C—H)51.09960.004 Å/C—O—O5105.260.5°/H—C—H5110.160.7°f(C—O—O—C)511964°
Product of moments of inertia:I AI BI C511233102117 g3 cm6.
10.1. Enthalpy of Formation
The enthalpy of formation of dimethyl peroxide re-commended in this work~2125.5 kJ mol21! was de-termined by Bakeret al.1 from calorimetric measurements ofthe enthalpy of combustion. Slightly lower values of
D fH° ~298.15 K! from 2129.3 kJ mol21 to 2133.9 kJ mol21
were estimated by group additivity2,3 and molecularmechanics calculations.4,5A lower value is estimatedfrom the experimental value ofD fH°(CH3O) Gurvichet al.6 and the bond energy for the O—O bond inCH3OOCH3:
7
504504 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
D fH°~CH3OOCH3!52D fH°~CH3O!
2D°~CH3O—OCH3!
52313– 16052134 kJ mol21.
A still more negative value,2138.1 kJ mol21, was proposedby Benassiet al.8 employing theoretical and empirical ap-proaches. Semiempirical MINDO9,10 and molecularmechanics11 calculations provideD fH° ~298.15 K! values,2105.1 to2121.6 kJ mol21, which are greater than the ex-perimental value. The available theoretical and empiricalevaluations are grounds to believe that the experimentalvalue of D fH° ~298.15 K! may be overestimated. Thus, itsuncertainty was increased in this work.
10.2. Heat Capacity and Entropy
The molecular structure of dimethyl peroxide,CH3OOCH3, was studied by electron diffraction.12 The mo-lecular intensities were analyzed using a model which con-sidered the internal rotation about the O—O bond. The equi-librium geometry was determined to be theskewconformation with a C—O—O—C dihedral angle of 119°.The barrier in the trans configuration (/C—O—O—C5180°) was found to be 87187/252 cm21. This result agreeswith an analysis of infrared and Raman spectra13 and a nor-mal coordinate analysis based on the these data14 as well aswith results of semiempirical,9,10,15,16ab initio17–19 and mo-lecular mechanics4,5,8 calculations. Photoelectron spectrainvestigations20,21 andab initio calculations8,22–24support anexactly planar or nearly planartransconfiguration. However,it should be noted that the value of a dihedral angle dependsstrongly on the basis set and method used.19 Hamada andMorishita25 have described the Raman and infrared spectraof CH3OOCH3 in terms of planar structure ofD3h symmetry.In this work, the product of the principal moments of inertiaof dimethyl peroxide forskewconformation ofC2 symmetrywas calculated using the structural parameters determinedfrom electron diffraction study.12
The dimethyl peroxide molecule undergoes three large-amplitude motions: an internal rotation of the OCH3 groupsabout the O—O bond and internal rotation of the CH3 groupsabout two C—O bonds. Contributions to the thermodynamicproperties from these hindered rotors were calculated in thiswork based on available data on the rotational barriers inCH3OOCH3. The value ofV35900 cm21 was accepted forthe internal rotation barrier of methyl groups around the C-Obonds. This value was used by Koput26 in his theoreticalmodel describing the internal rotation in dimethyl peroxideand it is the average of the results of molecular mechanicscalculations.4 The double-minimum potential energy func-tion,
V~w!5V01V1 cosw1V2 cos 2w1V3 cos 3w,
was used in this work for the internal rotation around theO—O bond. This function was chosen earlier for the hin-dered rotation potential function in hydrogen peroxide.27 Theexpansion coefficientsV0 , V1 , V2 , andV3 can be expressed
in terms of thetrans barrier heightVtrans , the cis barrierheightVcis , and the COOC dihedral anglewe correspondingto a minimum of the potential function.27 The values ofV0 ,V1 , V2 , and V3 were calculated in this work assumingVtrans587 cm21, Vcis54700 cm21, and we5119°. Thevalue of Vtrans was taken from the electron diffractionstudy.12 It agrees with results of theoretical calculations4,5,8,19
within the limits of experimental accuracy. The adoptedvalue ofVcis is based on results ofab initio8,18and molecularmechanics4,5 calculations. The values of the reduced mo-ments of inertia for CH3 and OCH3 tops were calculatedfrom structural parameters given above.
Christe13 has investigated the infrared spectra ofCH3OOCH3 and CD3OOCD3 both in the gas phase and in anAr matrix and the Raman spectra of these molecules in theliquid phase. The vibrational assignment proposed byChriste13 has considerable uncertainty for a number of thevibrations, and the low-frequency modes were not assignedat all. Bell and Laane14 have carried out a normal coordinateanalysis of dimethyl peroxide using the experimental data ofChriste.13 Hamada and Morishita25 have described the vibra-tional spectra of CH3OOCH3 in terms of D3h symmetry.However, this assignment is in conflict with available infor-mation on dimethyl peroxide. There are twoab initio calcu-lations of vibrational frequencies of CH3OOCH3.
23,28Resultsof Benassi and Taddei23 show overall agreement with experi-mental data taking into account the fact that theab initiofrequencies are unscaled and the anharmonicity contributionsare neglected. Chen and Allinger5 have carried out the mo-lecular mechanics calculation of vibrational frequencies ofdimethyl peroxide. Their results are in agreement with theavailable, but somewhat tentative and incomplete, experi-mental data.13 The assignment proposed by Chen andAllinger5 is accepted in this work.
The uncertainties in the calculated thermodynamic func-tions ~Table 9! may reach~2–4! J K21 mol21 for Cp°(T) and~3–5! J K21 mol21 for S°(T). They are caused by uncertain-ties in the adopted vibrational frequencies and the approxi-mate treatment of internal rotation.
Ideal gas thermodynamic properties of dimethyl peroxidehave not been reported previously.
10.3. References
1G. Baker, J. H. Littlefair, R. Shaw, and J. C. J. Thynne, J. Chem. Soc.6970 ~1965!.
2S. W. Benson, J. Chem. Phys.40, 1007~1964!.3S. W. Benson, J. Am. Chem. Soc.86, 3922~1964!.4L. Carballeira, R. A. Mosquera, and M. A. Rios, J. Comput. Chem.9, 851~1988!.
5K. Chen and N. L. Allinger, J. Comput. Chem.14, 755 ~1993!.6L. V. Gurvich, I. V. Veyts, and C. B. Alcock,Thermodynamic Propertiesof Individual Substances, 4th ed.~Hemisphere, New York, 1991!, Vol. 2.
7R. D. Bach, P. Y. Ayala, and H. B. Schlegel, J. Am. Chem. Soc.118,12758~1996!.
8R. Benassi, U. Folli, S. Sbardellati, and F. Taddei, J. Comput. Chem.14,379 ~1993!.
9C. Glidewell, J. Mol. Struct.67, 35 ~1980!.
505505NIST-JANAF THERMOCHEMICAL TABLES
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
10V. N. Kokorev, N. N. Vyshinskii, V. P. Maslennikov, I. A. Abronin, G.M. Zhidomirov, and Yu. A. Aleksandrov, Zh. Strukt. Khim.22, 9 ~1981!.
11W. H. Richardson, J. Org. Chem.54, 4677~1989!.12B. Haas and H. Oberhammer, J. Am. Chem. Soc.106, 6146~1984!.13K. O. Christe, Spectrochim. Acta A27, 463 ~1971!.14M. E. B. Bell and J. Laane, Spectrochim. Acta A28, 2239~1972!.15R. M. Minyaev, V. I. Minkin, I. I. Zakharov, and I. D. Sadekov, Teor.
Eksp. Khim.9, 816 ~1973!.16K. Ohkubo, T. Fujita, and H. Sato, J. Mol. Struct.36, 101 ~1977!.17B. Plesnicar, D. Kocjan, S. Murovec, and A. Azman, J. Am. Chem. Soc.
98, 3143~1976!.18W. Gase and J. E. Boggs, J. Mol. Struct.116, 207 ~1984!.19D. Christen, H. G. Mack, and H. Oberhammer, Tetrahedron44, 7363
~1988!.
20K. Kimura and K. Osafune, Bull. Chem. Soc. Jpn.48, 2421~1975!.21P. Rademacher and W. Elling, Liebigs Ann. Chem. 1473~1979!.22R. A. Bair and W. A. Goddard III, J. Am. Chem. Soc.104, 2719~1982!.23R. Benassi and F. Taddei, Tetrahedron50, 4795~1994!.24M.-B. Huang and H. U. Suter, J. Mol. Struct: THEOCHEM337, 173
~1995!.25K. Hamada and H. Morishita, Spectrosc. Lett.13, 185 ~1980!.26J. Koput, J. Mol. Spectrosc.141, 118 ~1990!.27R. H. Hunt, R. A. Leacock, C. W. Peters, and K. T. Hecht, J. Chem. Phys.
42, 1931~1965!.28G. A. Pitsevich, V. I. Gogolinskii, and I. P. Zyatkov, Zh. Prikl. Spektrosk.
56, 643 ~1992!.
TABLE 9. Ideal gas thermodynamic properties of dimethyl peroxide C2H6O2~g! at the standard state pressure,p°50.1 MPa (Tr5298.15 K)
aInstead of torsional moden18;70 cm21, the contributions due to theinternal rotation of O—CO—CH3 group around O—O bond were calcu-lated from the potentialV(w)5V01V1 cosw1V2 cos2w1V3 cos3w,wherew is the C—O—O—C torsional angle,V051433.9,V152222.2,V251111.1, andV35232.8~in cm21!.bInstead of torsional modesn19 andn36;60 cm21, the contributions dueto the internal rotation of CH3 groups around C—C bonds were calcu-lated from the potentialV(w)5 1
2V3(12cos 3w), where w is theH—C—C—O torsional angle andV3580 cm21.
O—CO—CH3 top: Reduced moment of inertia,I r54.5200310239 g cm2, Symmetry number,sm51.
CH3 top: Reduced moment of inertia,I r50.5182310239 g cm2, Symmetry number,sm53.
Geometryr ~C—C!51.49560.01 Å /OvC—O512263°r ~CvO!51.2160.02 Å /C—O—O511363°r ~C—O!51.3460.02 Å /H—C—H5109.562.0°r ~O—O!51.4660.02 Å w~C—O—O—C!5120610°r ~C—H!51.0960.01 Å w~OvC—O—O!50°/C—CvO512863°
Product of moments of inertia:I AI BI C5960753102117 g3 cm6.
507507NIST-JANAF THERMOCHEMICAL TABLES
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
11.1. Enthalpy of Formation
Jaffeet al.1 determined the enthalpy of formation for liq-uid diacetyl peroxide (CH3CO—OO—COCH3) from calori-metric measurements. Assuming the enthalpy of vaporizationof diacetyl peroxide to be equal to the enthalpy of vaporiza-tion of acetic anhydride (CH3CO—O—COCH3), the authorsobtained the value of2498 kJ mol21 for the enthalpy offormation of gaseous diacetyl peroxide. A similar value ofD fH°(298.15 K)52502 kJ mol21 may be derived from thegroup additivity contributions for peroxyacids and peroxyes-ters obtained by Benassi and Taddei2 using empirical ap-proaches andab initio calculations. The value predicted bythe method of group equations,
D fH°~CH3CO—OO—COCH3!
5D fH°~CH3CO—O—COCH3!1D fH°~CH3OOCH3!
2D fH°~CH3OCH3!5~2572.5!1~2125.5!
2~2184.1!52513.9
~theD fH° values for the related compounds were taken fromthe compilation by Pedley3!, agrees with the two above esti-mates within the limits of the combined errors of those de-terminations. Considerably lower values ofD fH° for di-acetyl peroxide were estimated from a group additivityapproximation~2540 kJ mol21!4 and a semiempirical calcu-lation ~;2585 kJ mol21!.5,6 The value recommended in thiswork, 2(500610) kJ mol21, is based on the estimates.1,2
11.2. Heat Capacity and Entropy
Experimental data on molecular structure and vibrationalfrequencies of diacetyl peroxide, CH3CO—OO—COCH3,are unknown. Semiempirical MINDO calculations5 predictthat the skew conformation of C2 symmetry with aC—O—O—C dihedral angle of 108° is the most stable. Al-though a planar structure was suggested for the peroxy acidgroup in peroxyacetic acid from a microwave study,7 theskewconformation ofC2 symmetry is accepted in this workfor diacetyl peroxide in accord with a semiempiricalcalculation5 and by analogy with dimethyl peroxide.8 Theproduct of the principal moments of inertia was calculated
from structural parameters estimated by comparison withstructural parameters of CH3CO—OOH,7
CH3CO—O—COCH3,9 and CH3OOCH3.
8
The diacetyl peroxide molecule undergoes five large-amplitude motions: an internal rotation about a central O—Obond and about two C—C and two C—O bonds. Contribu-tions to the thermodynamic functions due to internal rotationof CH3 groups were calculated in this work assuming theV3
barrier height to be the same as that in peroxyacetic acid.7
The double-minimum potential energy function,
V~w!5V01V1 cosw1V2 cos 2w1V3 cos 3w,
was used for the internal rotation about the O—O bond. Thisfunction was chosen earlier for the hindered rotation poten-tial function in hydrogen peroxide.10 The expansion coeffi-cientsV0 , V1 , V2 , andV3 can be expressed in terms of thetrans barrier heightVtrans , the cis barrier heightVcis , andthe COOC dihedral anglewe corresponding to a minimum ofthe potential function.10 The values ofV0 , V1 , V2 , andV3
were calculated in this work assumingVtrans590 cm21,Vcis55000 cm21, and we5120°. The values ofVtrans andVcis are derived from the results of a MINDO calculation5
taking into account that the same calculation overestimatedthe Vtrans and underestimated theVcis barriers for theCH3OOH and CH3OOCH3 molecules. The values of the re-duced moments of inertia for CH3 and CH3COO tops werecalculated from structural parameters given above. There areno data on barriers hindering the internal rotation of CH3COgroups about the C-O bonds. Frequenciesn175151 andn35
5140 cm21 were accepted in this work for the torsionalmotion about the C-O bonds.
Zyatkovet al.11 have calculated vibrational frequencies ofdiacetyl peroxide using a theoretical simulation of the forcefield. In this work, vibrational frequencies ofCH3CO—OO—COCH3 were calculated using force con-stants transferred from the CH3CO—OOH molecule. Thesimplified valence force field for that molecule was obtainedby normal coordinate calculations for the vibrational assign-ment of Cugleyet al.12 The calculated force constants repro-duce the observed vibrational wave numbers ofCH3CO—OOH with a root mean square deviation of 0.6cm21. The following 18 force constants were used for calcu-lating the vibrational frequencies of diacetyl peroxide:
f O—O 3.821 f C—C—O 2.363 f tors~C—O! 0.430
f C—O 3.827 f OvC—O5 f OvC—C 1.972 f tors~O—O! 0.104
f CvO 11.382 f C—C—H 0.497 f CvO,C—C5 f CvO,C—O 1.679
f C—C 3.480 f H—C—H 0.523 f C—C,C—O 20.356
f C—H 4.836 f wag~CvO! 0.515 f C—H,C—C—H 0.415
f C—O—O 1.659 f tors~C—C! 0.006 f C—O,OvC—O 0.232
508508 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
~stretching and stretch-stretch interaction constants are inunits of mdyn/Å; bending, wagging, and torsion constantsare in units of mdyn Å; stretch-bend interaction constants arein units of mdyn!.
The uncertainties in the calculated thermodynamic func-tions ~Table 10! may reach~8–12! J K21 mol21 for Cp°(T)and ~6–10! J K21 mol21 for S°(T). They are caused by theuncertainties in the adopted vibrational frequencies and theapproximate treatment of internal rotation.
Ideal gas thermodynamic properties of diacetyl peroxidehave not been reported previously.
11.3. References
1L. Jaffe, E. L. Prosen, and M. Szware, J. Chem. Phys.27, 416 ~1957!.2R. Benassi and F. Taddei, J. Mol. Struct.: THEOCHEM303, 101 ~1994!.
3J. B. Pedley,Thermochemical Data and Structures of Organic Com-pounds~Thermodynamics Research Center, College Station, TX, 1994!,Vol. I.
4S. W. Benson, F. R. Cruickshank, D. M. Golden, G. R. Haugen, H. E.O’Neal, A. S. Rodgers, R. Shaw, and R. Walsh, Chem. Rev.69, 279~1969!.
5C. Glidewell, J. Mol. Struct.67, 35 ~1980!.6V. N. Kokorev, N. N. Vyshinskii, V. P. Maslennikov, I. A. Abronin, G.M. Zhidomirov, and Yu. A. Aleksandrov, Zh. Strukt. Khim.22, 9 ~1981!.
7J. A. Cugley, W. Bossert, A. Bauder, and H. H. Gu¨nthard, Chem. Phys.16, 229 ~1976!.
8B. Haas and H. Oberhammer, J. Am. Chem. Soc.106, 6146~1984!.9H. J. Vledder, F. C. Mijlhoff, J. C. Leyte, and C. Romers, J. Mol. Struct.7, 421 ~1971!.
10R. H. Hunt, R. A. Leacock, C. W. Peters, and K. T. Hecht, J. Chem. Phys.42, 1931~1965!.
11I. P. Zyatkov, V. I. Gogolinskii, V. V. Sivchik, and D. I. Sagaidak, Zh.Prikl. Spektrosk.29, 652 ~1978!.
12J. A. Cugley, R. Meyer, and H. H. Gu¨nthard, Chem. Phys.18, 281~1976!.
TABLE 10. Ideal gas thermodynamic properties of diacetyl peroxide, C4H6O4~g! at the standard state pressure,p°50.1 MPa (Tr5298.15 K)
The thermodynamic properties of 10 organic moleculeshave been calculated, based on the critical evaluation ofavailable thermodynamic and spectroscopic information.Where no data were available, estimation techniques wereused. Recommended values for the entropy, heat capacity,and the enthalpy of formation at 298.15 K are summarized inTable 11.
For a first round of new experimental studies, substantiallyimproved formation properties could be obtained with newor confirming measurements for the enthalpy of formationfor bromoacetic acid, glycolic acid, the cyanooxomethylradical, and the three peroxides—methyl hydroperoxide,dimethyl peroxide, and diacetyl peroxide. In order to calcu-late significantly more reliable thermal functions, the struc-ture and the vibrational frequencies are needed for the cya-nooxomethyl radical and diacetyl peroxide, since these datawere estimated for these two compounds.
13. Acknowledgments
The authors wish to acknowledge the support of this workby the Upper Atmospheric Research Program of the NationalAeronautics and Space Administration~NASA! and theStandard Reference Data~SRD! Program of the National In-stitute of Standards and Technology~NIST!. The authorsthank Professor Joel Liebman of the University of Maryland,Baltimore County, for bringing to their attention the just-published work, so relevant to this article, of the 10 scientistsof Portugal and Germany working with Professor Manuel E.Minas da Piedade of the Centro de Quı´mica Estrutural, Com-plexo Interdisciplinar, at the Institutio Superior Te´cnico, Lis-bon, Portugal. The authors are also grateful to ProfessorVladimir Yungman of the Institute for High Temperatures~IVTAN ! of the Russian Academy of Sciences, Dr. MalcolmW. Chase of SRD, and Dr. Eugene S. Domalski of NISTwhose expert advice, support, and encouragement were es-sential to the completion of this project.
14. Extended Bibliographies
The following bibliography lists articles that were found in the literature pertaining to the molecules discussed above butwere not used as sources of information in the evaluations.
14.1. Extended Bibliography for Bromoacetic Acid, C 2H3BrO2
71KIN/GOL King, K. D., Golden, D. M., and Benson, S. W., ‘‘Thermochemistry of the gas-phase equilibriumCH3COCH31Br25CH3COCH21HBr,’’ J. Chem. Thermodyn.3, 129–134~1971!.
78VAN/BRA Van Eijck, B. P., Brandts, P., Maas, J. P. M., ‘‘Microwave spectra and molecular structures of rotationalisomers of fluoroacetic acid and fluoroacetyl fluoride,’’ J. Mol. Struct.44, 1–13~1978!.
93CAR/LAY Carson, A. S., Laye, P. G., Pedley, J. B., Welsby, A. M., ‘‘The enthalpies of formation of iodomethane,diiodomethane, triiodomethane, and tetraiodomethane by rotating combustion calorimetry,’’ J. Chem. Ther-modyn.25, 261–269~1993!.
14.2. Extended Bibliography for Chloroacetic Acid, C 2H3ClO2
64JOH Johansen, H., ‘‘Normal coordinate analysis of polyatomic molecules and statistical thermodynamics ofisotopic molecules,’’ Z. Phys. Chem.227, 305–328~1964!.
75CHA/DEV Chandramani, R., Devaraj, N., ‘‘Torsional-vibration frequency ina-CH2ClCOOH and its temperature de-pendence from pure quadrupole resonance measurements,’’ Indian J. Pure Appl. Phys.13, 637–638~1975!.
75SIN/KAT Sinha, D., Katon, J. E., Jakobsen, R. J., ‘‘The vibrational spectra and structure ofb- and g-chloroaceticacid,’’ J. Mol. Struct.24, 279–291~1975!.
TABLE 11. Summary of the thermodynamic properties at 298.15 K and the standard state pressure,p°50.1 MPa
86FAU/TEI2 Fausto, R., Teixeira-Dias, J. J. C., ‘‘Conformational and vibrational spectroscopic analysis of CHCl2COXand CCl3COX ~X5Cl, OH, OCH3!,’’ J. Mol. Struct. 144, 241–263~1986!.
93KUL/FAU Kulbida, A., Fausto, R., ‘‘Conformers, vibrational spectra and infrared-induced rotamerization of dichloro-acetic acid in argon and krypton matrixes,’’ J. Chem. Soc., Faraday Trans.89, 4257–4266~1993!.
96NYQ/CLA Nyquist, R. A., Clark, T. D., ‘‘Infrared study ofa-haloacetic acids in solution,’’ Vib. Spectrosc.10, 203–228~1996!.
14.3. Extended Bibliography for Oxopropanedinitrile, C 3N2O
53KEM/TRA Kemula, W., Tramer, A., ‘‘Vibrational specrum of carbonyl cyanide,’’ Roczniki Chem.27, 522–523~1953!.70NAY/ARU Nayar, V. U., Aruldhas, G., ‘‘Force field and Coriolis coupling coefficients of carbonyl cyanide,’’ Indian J.
Pure Appl. Phys.8, 840–841~1970!.71DUN/WHI Duncan, A. B. F., Whitlock, R. F., ‘‘Vacuum ultraviolet absorption spectrum of carbonyl cyanide,’’ Spec-
trochim. Acta A27, 2539–2541~1971!.72NAY/ARU Nayar, V. U., Aruldhas, G., Joseph, K. B., Cyvin, S. J., ‘‘Vibrational analyses and mean amplitudes for some
simple molecules. III. Carbonyl cyanide,’’ Mol. Struct. Vib. 237–242~1972!.97LER/DEW Leroy, G., Dewispelaere, J. P., Wilante, C., Benkadour, H., ‘‘A theoretical approach to the thermochemistry
of the polymerization of some derivatives of the monomers CH25X ~X5CH2, NH, O!,’’ Macromol. TheorySimul. 6, 729–739~1997!.
97MED/BHA Medhi, C., Bhattacharyya, S. P., ‘‘Transcription of the results of quantum calculations in terms of theclassical notion of molecular structures: The cases of some small carbonyls in the ground and excitedstates,’’ Proc. Indian Acad. Sci., Chem. Sci.109, 61–70~1997!.
14.4. Extended Bibliography for Glycolic Acid, C 2H4O3
87KAK Kakumoto, T., ‘‘A theoretical study on the unimolecular decomposition of somea-dicarbonyl compounds:glyoxal, oxalic acid and glycolic acid,’’ J. Sci. Hiroshima Univ. A51, 69–111~1987!.
93DOM/HEA Domalski, E. S., Hearing, E. D., ‘‘Estimation of the thermodynamic properties of C-H-N-O-S-halogencompounds at 298.15 K,’’ J. Phys. Chem. Ref. Data22, 805–1159~1993!.
14.5. Extended Bibliography for Glyoxal, C 2H2O2
39LUV/SCH LuValle, J. E., Schomaker, V., ‘‘The molecular structures of glyoxal and dimethyl glyoxal by the electrondiffraction method,’’ J. Am. Chem. Soc.61, 3520–3525~1939!.
49COL/THO Cole, A. R. H., Thompson, H. W., ‘‘Vibration-rotation bands of some polyatomic molecules,’’ Proc. R. Soc.London, Ser. A,200, 10–20~1949!.
54BRA/MIN Brand, J. C. D., Minkoff, G. J., ‘‘The infrared spectrum of dideuteroglyoxal,’’ J. Chem. Soc. 2970–2971~1954!.
64COL/OSB Cole, A. R. H., Osborne, G. A., ‘‘Fundamentaln12 of glyoxal,’’ J. Chem. Soc. 1532~1964!.69JEN/HAG Jensen, H. H., Hagen, G., Cyvin, S. J., ‘‘Mean amplitudes of vibration for some conjugated carbonyl
compounds: glyoxal, acrolein, andp-benzoquinone,’’ J. Mol. Struct.4, 51–58~1969!.71AGA/BAI Agar, D. M., Bair, E. J., Birss, F. W., Borrell, P., Chen, P. C., Currie, G. N., McHugh, A. J., Orr, B. J.,
Ramsay, D. A., Roncin, J. Y.,‘‘The 4550 Å band system of glyoxal. III. Vibration-rotational analyses for 11bands of C2D2O2,’’ Can. J. Phys.49, 323–327~1971!.
73DON/RAM Dong, R. Y., Ramsay, D. A., ‘‘A band system of glyoxal-d1 and glyoxal-d2 ,’’ Can. J. Phys.51, 1463–1465~1973!.
73GLE/MCC Gleghorn, J. T., McConkey, F. W., ‘‘The structure and properties of carbonyl compounds,’’ J. Mol. Struct.18, 219–225~1973!.
73LE/TYU Le, H. H., Tyulin, V. I., ‘‘Raman spectrum of liquid glyoxal (C2O2H2),’’ Opt. Spektrosk.35, 770–772~1973!.
75COL/DUR Cole, A. R. H., Durig, J. R., ‘‘Raman and infrared spectra of solid glyoxal-d1 and glyoxal-d2 ,’’ J. RamanSpectrosc.4, 31–39~1975!.
75GUT/BAU Gut, M., Bauder, A., Gu¨nthard H. H., ‘‘Solution of the rotation-internal rotation problem of glyoxal typemolecules by infinite matrix technique,’’ Chem. Phys.8, 252–271~1975!.
75PAN Pancir, J., ‘‘Cis-transisomerization of glyoxal. A contribution to the rehabilitation of semiempirical meth-ods,’’ Theor. Chim. Acta40, 81–83~1975!.
76COL/CRO Cole, A. R. H., Cross, K. J., Ramsay, D. A., ‘‘Rotational structure of the~0–0! visible band of glyoxal-d1 .A reanalysis,’’ J. Phys. Chem.80, 1221–1223~1976!.
511511NIST-JANAF THERMOCHEMICAL TABLES
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
76DEV/TOW Devaquet, A. J. P., Townshend, R. E., Hehre, W. J., ‘‘Conformational studies of 1,3-dienes,’’ J. Am. Chem.Soc.98, 4068–4076~1976!.
77VON Von Niessen, W., ‘‘Trans- andcis-glyoxal: A Green’s function calculation on their photoelectron spectra,’’J. Am. Chem. Soc.99, 7151–7153~1977!.
78COS/FRA Cossart-Magos, C., Frad, A., Tramer, A., ‘‘Fluorescence and phosphorescence spectra of glyoxal-h2 and -d2
from single vibronic levels of1Au and3Au states,’’ Spectrochim. Acta A34, 195 ~1978!78LUC/SCH Lucchese, R. R., Schaefer, H. F., III, ‘‘Formulation of the direct configuration interaction method for triplet
spin states. Application to glyoxal,’’ J. Chem. Phys.68, 769–774~1978!.78PAR/ROR Parmenter, C. S., Rordorf, B. F., ‘‘Fluorescence from selected rotational levels ofS1 glyoxal,’’ Chem. Phys.
27, 1–9 ~1978!.79MOR/MAK Morozov, A. A., Makhnev, A. S., Panchenko, Y. N., Stepanov, N. F., ‘‘Calculation of some molecular
parameters of glyoxal,’’ Vestn. Mosk. Univ., Ser. 2: Khim.20, 326–331~1979!.81NGU/TRO Nguyen-Xuan, T., Tronchet, J. M. J., Bill, H., ‘‘Conformational equilibriums of carbohydrates on the level
of sC(sp2),C(sp3) bonding. IX. Study of the factors affecting the conformational equilibrium ofE-1,3-disubstituted propenes using energy partitioning techniques,’’ Helv. Chim. Acta64, 1949–1958~1981!.
81OSA/SHA Osamura, Y., Shaefer, H. F. III, Dupuis, M., Lester, W. A., Jr., ‘‘A unimolecular reaction ABC→A1B1Cinvolving three product molecules and a single transition state. Photodissociation of glyoxal:HCO—HCO→H21CO1CO,’’ J. Chem. Phys.75, 5828–5836~1981!.
82BOC/TRA Bock, C. W., Trachtman, M., George, P., ‘‘Anab initio study of the geometry of the C—C~H!vO group, thef C—C2 stretching force constant, and thef CvO,C—C coupling constant in conjugated monosubstituted carbonylcompounds,’’ Chem. Phys.68, 143–154~1982!.
83PAN/MOC Panchenko, Y. N., Mochalov, V. I., Pentin, Y. A., ‘‘Calculation of potential curves of the internal rotation ofglyoxal and its fluoro derivatives in the CNDO/2 approximation taking into account a change in geometry,’’Vestn. Mosk. Univ., Ser. 2: Khim.24, 357–360~1983!.
85MUS/FIG Musso, G. F., Figari, G., Magnasco, V., ‘‘Improved bond-orbital calculations of rotation barriers in mol-ecules containing conjugated double bonds and/orp lone pairs,’’ J. Chem. Soc., Faraday Trans. 281,1243–1258~1985!.
86DUV/KIN Duval, A. B., King, D. A., Haines, R., Isenor, N. R., Orr, B. J., ‘‘Coherent Raman spectroscopy of glyoxalvapor,’’ J. Raman Spectrosc.17, 177–182~1986!.
86SPA/PRA Spangler, L. H., Pratt, D. W., Birss, F. W., ‘‘Rotational analysis of some vibronic bands in the3Au21Ag
transition of glyoxal. Spin splittings in the lowest triplet state of the isolated molecule,’’ J. Chem. Phys.85,3229–3236~1986!.
87PEB/JOS Pebay Peyroula, E., Jost, R., ‘‘S1←S0 laser excitation spectra of glyoxal in a supersonic jet: Vibrationalanalysis,’’ J. Mol. Spectrosc.121, 177–188~1987!.
87ROD/OLD Rodler, M., Oldani, M., Grassi, G., Bauder, A., ‘‘Rotational spectra of s-trans and s-cis glyoxal-d1
(CHO—CDO) observed by microwave Fourier transform spectroscopy,’’ J. Chem. Phys.87, 5365–5369~1987!.
88FAB Fabian, W. M. F., ‘‘AM1 calculations of rotation around essential single bonds and preferred conformationsin conjugated molecules,’’ J. Comput. Chem.9, 369–377~1988!.
89BRI Brinn, I. M., ‘‘Fundamental vibrational frequency correlation. IV.C2v2C2h in-plane trends,’’ Spectrochim.Acta A 45, 653–659~1989!.
89MOH/PAY Mohan, S., Payami, F., Kuttiappan, P., ‘‘Laser Raman spectrum of glyoxal and its vibrational analysis,’’Proc. Indian Natl. Sci. Acad. A55, 598–601~1989!.
92WIB/RAB Wiberg, K. B., Rablen, P. R., Marquez, M., ‘‘Resonance interactions in acyclic systems. 5. Structures, chargedistributions, and energies of some hetrobutadiene rotamers,’’ J. Am. Chem. Soc.114, 8654–8668~1992!.
95MO/ZHA Mo, Y., Zhang, Q., ‘‘Why N2O2 is cis while (CHO)2 is trans: MO and VB studies,’’ Int. J. Quantum Chem.56, 19–26~1995!.
96PRO/SHO Promyslov, V. M., Shorygin, P. P., ‘‘Quantum-chemical study of conjugation in molecules containingconjugated CvC and CvO bonds,’’ Izv. Akad. Nauk, Ser. Khim. 1648–1652~1996!.
97REM/WAT Rempe, S. B., Watts, R. O., ‘‘The convergence properties of hindered rotor energy levels,’’ Chem. Phys.Lett. 269, 455–463~1997!.
14.6. Extended Bibliography for Cyanooxomethyl Radical, NC 2O
91GUR/VEY Gurvich, L. V., Veyts, I. V., Alcock, C. B.,Thermodynamic Properties of Individual Substances, 4th ed.~Hemisphere, New York, 1991!, Vol. 2.
512512 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
92DOR/GUR Dorofeeva, O. V., Gurvich, L. V., ‘‘Thermodynamic properties of linear carbon chain molecules withconjugated triple bonds. Part 2. Free radicals CnH (n52 – 12) and CnN (n52 – 11),’’ Thermochim. Acta197, 53–68~1992!.
94PED Pedley, J. B.,Thermochemical Data and Structures of Organic Compounds~Thermodynamics ResearchCenter, College Station, TX, 1994!, Vol. I.
14.7. Extended Bibliography for Oxalic Acid, C 2H2O4
26VER/HAR Verkade, P. E., Hartman, H., Coops, J., ‘‘Calorimetric researches. X. Heats of combustion of successiveterms of homologous series: Dicarboxylic acids of the oxalic acid series,’’ Recl. Trav. Chim.45, 373–393~1926!.
78DEV/NOV De Villepin, J., Novak, A., Romain, F., ‘‘Vibrational spectra of oxalic acids. II. IR and Raman spectra of thea-phase of oxalic acid, and its deuterium and oxygen-18 derivatives,’’ Spectrochim. Acta A34, 1019–1024~1978!.
80SHI Shippey, T. A., ‘‘Vibrational studies in aqueous solutions. Part I. The oxalate ion,’’ J. Mol. Struct.65, 61–70~1980!.
95CHE/CHE Chen, L.-T., Chen, G.-J., Fu, X.-Y., ‘‘Theoretical studies on the mechanism of the thermal decarboxylationand decarbonylation of a number ofa-ketoacids,’’ Chin. J. Chem.13, 487–492~1995!.
14.8. Extended Bibliography for Methyl Hydroperoxide, CH 4O2
79MOL/ARG Molina, M. J., Arguello, G., ‘‘Ultraviolet absorption spectrum of methyl hydroperoxide vapor,’’ Geophys.Res. Lett.6, 953–955~1979!.
96GRE/COL Grela, M. A., Colussi, A. J., ‘‘Quantitative structure-stability relationships for oxides and peroxides ofpotential atmospheric significance,’’ J. Phys. Chem.100, 10150–10158~1996!.
96JUR/MAR Jursic, B. S., Martin, R. M., ‘‘Calculation of bond dissociation energies for oxygen containing molecules byab initio and density functional theory methods,’’ Int. J. Quantum Chem.59, 495–501~1996!.
97JAC/WEH Jacob, P., Wehling, B., Hill, W., Klockow, D., ‘‘Feasibility study of Raman spectroscopy as a tool toinvestigate the liquid-phase chemistry of aliphatic organic peroxides,’’ Appl. Spectrosc.51, 74–80~1997!.
14.9. Extended Bibliography for Dimethyl Peroxide, C 2H6O2
82BAT/WAL Batt, L., Walsh, R., ‘‘A reexamination of the pyrolysis of bis trifluoromethyl peroxide,’’ Int. J. Chem. Kinet.14, 933–944~1982!.
92ZYA/KNY Zyatkov, I. P., Knyazhevich, N. D., Gogolinskii, V. I., Pitsevich, G. A., ‘‘Quantum-chemical calculations onstructure and conformations of organosilicon peroxides,’’ Vestn. Beloruss. Gos. Univ., Ser. 1, No. 2, 33–37~1992!.
96LEE/SHI Lee, S.-Y., Shin, Y.-J., ‘‘Estimation of thermodynamic properties in the pyrolysis of dialkyl peroxides inhelium gas,’’ Hwahak Konghak34, 592–596~1996!.
14.10. Extended Bibliography for Diacetyl Peroxide, C 4H6O4
71VLE/MIJ Vledder, H. J., Mijlhoff, F. C., Leyte, J. C., Romers, C., ‘‘Electron diffraction investigation of the molecularstructure of gaseous acetic anhydride,’’ J. Mol. Struct.7, 421–429~1971!.
80HOL/GUN Hollenstein, H., Gu¨nthard, H. H., ‘‘A transferable valence force field for polyatomic molecules. A schemefor a series of molecules containing carbon:oxygen groups,’’ J. Mol. Spectrosc.84, 457–477~1980!.
81VAN/VAN Van Eijck, B. P., van Opheusden, J., van Schaik, M. M. M., van Zoeren, E., ‘‘Acetic acid: Microwavespectra, internal rotation and substitution structure,’’ J. Mol. Spectrosc.86, 465–479~1981!.
93CHE/ALL Chen, K., Allinger, N. L., ‘‘A molecular mechanics study of alkyl peroxides,’’ J. Comput. Chem.14,755–768~1993!.
94BEN/TAD Benassi, R., Taddei, F., ‘‘Conformational properties of peroxyacids, peroxyesters and structurally relatedradicals: A theoreticalab initio MO approach,’’ J. Mol. Struct.: THEOCHEM303, 83–100~1994!.
96JON Jonsson, M., ‘‘Thermochemical properties of peroxides and peroxyl radicals,’’ J. Phys. Chem.100, 6814–6818 ~1996!.