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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 RuAcademy of Sciences, IVTAN Association of the RAS, Izhorskaya13/19, 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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
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1. Introduction
A large number of biogenic and industrial polutant specplay a direct or indirect role in tropospheric smog chemistModeling of the kinetics of tropospheric chemical reactiprocesses often requires thermodynamic data. In the folling, evaluated thermodynamic data for a few smaller orgaspecies including some peroxides relevant to smog chemand atmospheric chemistry in general are presented.
The ideal gas thermodynamic properties of the polyatommolecules were calculated by standard statistical mechanmethods in which a rigid-rotor harmonic-oscillator modemodified where appropriate for internal rotations, wassumed for each compound. The statistical formulas for thmodynamic functions are discussed in several textbooksview articles, and reference books.1–6 Molecular andspectroscopic constants needed for the calculations werelected from the literature. In a few cases missing data westimated by analogy to related compounds. For some mecules, the fundamental frequencies were estimated bymal coordinate calculations using force constants transfefrom related molecules and the program NCA writtenNovikov and Malyshev.7
To evaluate the internal rotational contributions to tthermodynamic functions, the internal rotational partitifunction was formed by the summation of internal rotationenergy levels for each rotor. These energy levels weretained by the diagonalization of the one dimensional Hamtonian using a potential function of the form
V~w!51
2 (n
Vn~12cosnw!, ~1!
wherew is the internal rotational angle. The method of geerating the internal rotation energy levels has been descrby Lewis et al.8,9 The constant required to generate theternal rotational energy levels for each rotor is the interrotational constant~F ! or reduced moment of inertia of throtating group (I r). Where available, theVn terms and inter-nal rotational constant were taken from spectroscopic datthe F value was unavailable, it was calculated from theduced moment of inertia with the relationship
F5h/8p2cIr . ~2!
The value ofI r was calculated using molecular structurparameters with a computer program based on a methocalculating the reduced moments of inertia developedPitzer and Gwinn.10,11
A molecular model of an equilibrium mixture oftransandcis isomers was employed for calculating the thermodynamfunctions of glyoxal.4,12,13This method uses the enthalpy diference between the two conformers to calculate the equrium mole fraction of each species. From these datathermodynamic functions of two conformers, values of thmodynamic functions were calculated, allowing for the ming of two conformers.
The sources of uncertainties in the calculated thermonamic functions arise from uncertainties in the molecu
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477477NIST-JANAF THERMOCHEMICAL TABLES
constants used in the calculations as well as deviations fthe rigid-rotor harmonic-oscillator model. In this work thuncertainties in the thermodynamic functions were estimaby the procedure developed by Gurvichet al.6 This approachpredicts the uncertainties in the thermodynamic functioS°(T) andCp°(T) for simple molecules such as C3N2O rea-sonably well. For molecules with one or more internal rotions, the additional uncertainties due to deviations fromrigid-rotor harmonic-oscillator model are difficult to asseThe largest uncertainty probably arises from the anharmoity of the asymmetric torsion. This will have little effect aroom temperature but may be significant at the higher teperatures. The total estimated uncertainties in the thermonamic functionsS°(T) and Cp°(T) in the range between298.15 and 2000 K are given in the discussions for emolecule.
Based on the selected values of the molecular constathe ideal gas thermodynamic functions, heat capacCp°(T), entropy, S°(T), enthalpy @H°(T)2H°(298.15 K)#, and the Gibbs energy functio$2@G°(T)2H°(298.15 K)#/T%, have been calculated foselected temperatures up to 2000 K at the standard statesure,p°50.1 MPa.~In the tables that follow in a few caseexcited electronic states have been factored into the calctions; the energy of an electronic state relative to the groelectronic state is given as«G ; the degeneracy of electronistates are referred to in these tables as the ‘‘quanweight,’’ gG.) The enthalpy of formation value@D fH°(298.15 K)# were selected by analyzing experimenstudies which may result in the enthalpies of formationtermination. In the absence of experimental data,D fH°(298.15 K) values were estimated by approximamethods accepted as standard for organic moleculesradicals.14,15
The calculated values of the enthalpy difference,@H°(T)2H°(298.15 K)#, and entropy,S°(T), of the ideal gas were
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combined with values of the enthalpies and entropies ofelements in their reference states to derive values of enthof formation (D fH°), Gibbs energy of formation (D fG°),and the logarithm of the equilibrium constant of formatio(logKf°) of the substances as a function of temperature othe 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, NJ1953!.
2J. G. Aston and J. J. Fritz,Thermodynamics and Statistical Thermodynaics ~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.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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478478 DOROFEEVA, NOVIKOV, AND NEUMANN
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.
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2.1. Enthalpy of Formation
The recommended value of enthalpy of formationgaseous bromoacetic acid,2(383.563.1) kJ mol21, wasobtained by Lagoaet al.1 from experimental measurementThis value is the sum of the enthalpy of formationbromoacetic acid in the crystalline state,D f H°(C2H3BrO2,
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and the enthalpy of sublimation,DsubH°~C2H3BrO2)5(83.5062.95) kJ mol21, determined from Knudseneffusion experiments. Note that the recommended valuclose to the value predicted by the method of groequations:2
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479479NIST-JANAF THERMOCHEMICAL TABLES
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 formatiof 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 spec(CH2
79BrCOOH, CH281BrCOOH, and CH2
79BrCOOD!.Although no complete structure could be evaluated fromavailable data, the substitution coordinates of the Br atand 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 chloracetic 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 geometry of chloroacetic acid calculated by Chenet al.6 wasalso not consistent with that determined from experimenstudies. The trans structure with respect to the atomBr—C—C—O—H ~Cs symmetry! is accepted in this workfor lowest-energy conformer of bromoacetic acid in accowith the microwave data.5 The isotope-weighted value of thproduct of the principal moments of inertia of bromoaceacid is calculated in this work from the rotational constafor CH2
79BrCOOH and CH281BrCOOH.5 Structural param-
eters given above are those estimated by comparisonstructural parameters of CH3COOH,7 CH2ClCH3,
8
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CH2ClCOOH,9 and CH2BrCH3.10 These structural param
eters yield values for the rotational constants which1.2%–1.6% different from the observed values used incalculations. The difference has a negligible effect onthermodynamic functions.
There is no information on other stable conformers of bmoacetic 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 enerthan thetransconformation. Their rough estimate of the tosional frequency, 47 cm21, may be compared with 62 cm21
for chloroacetic acid.11 As in the case of chloroacetic acidthe simple potential,
V~w!5 12V3~12cos 3w!,
wherew is the Br—C—CvO torsional angle, is used in thiwork to calculate the internal rotational contributions to tthermodynamic functions of bromoacetic acid. The barrheight 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 acceptedbe the same as that for chloroacetic acid. The value ofreduced moment of inertia for the CH2Br top was derivedfrom structural parameters adopted in this work~see above!.
Vibrational spectra of bromoacetic acid were investigaonly for a solid phase.14–17These vibrational assignments aincomplete and it may be expected that they are muchferent from a gaseous spectrum as in the case of chloroaacid. Fundamental frequencies of gaseous bromoaceticwere estimated in this work by normal coordinate calcutions using the force constants transferred from related cpounds. Simplified force fields for CH3COOH, CH2ClCH3,CH2BrCH3, and CH2ClCOOH were determined using experimental vibrational assignments for these molecules.18–21
37 force constants were used to calculate the vibrationalquencies 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
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480480 DOROFEEVA, NOVIKOV, AND NEUMANN
~stretching and stretch–stretch interaction constants arunits of mdyn/Å; bend, wagging, and torsion constants arunits of mdyn Å; stretch–bend interaction constants areunits of mdyn!. These constants were transferred froCH3COOH and CH2BrCH3 molecules with corrections madby analyzing the trends in force constants of molecuCH3COOH, CH2ClCH3, and CH2ClCOOH.
The uncertainties in the calculated thermodynamic futions ~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 uncertainties in the adopted vibrational frequencies and theproximate treatment of internal rotation.
Ideal gas thermodynamic properties of bromoacetic ahave not been reported previously.
2.3. References
1A. L. C. Lagoa, H. P. Diogo, M. Pilar Dias, M. E. Minas da Piedade,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.7,483 ~2001!.
2D. R. Stull, E. F. Westrum, and G. C. Sinke,The Chemical Thermodynamics of Organic Compounds~Krieger, Malabar, FL, 1987!; see also the‘‘difference method,’’ N. Cohen, and S. W. Benson, Chem. Rev.93, 2419~1993!.
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ininn
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3J. B. Pedley,Thermochemical Data and Structures of Organic Compounds~Thermodynamics Research Center, College Station, TX, 19!,Vol. I.
4S. G. Lias, J. E. Bartmess, J. F. Liebman, J. L. Holmes, R. D. Levin,W. 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. vZoeren, 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. Ph
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!.
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481481NIST-JANAF THERMOCHEMICAL TABLES
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.
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3.1. Enthalpy of Formation
The recommended value of the enthalpy of formationgaseous chloroacetic acid at 298.15 K is the sum of thethalpy of formation of thea form of the solid and the enthalpy of sublimation both at 298.15 K. The valueD fH°(298.15 K,a-cr)52(509.7460.49) kJ mol21 is fromthe work of Lagoaet al.1 who measured the enthalpy ocombustion of thea form of the solid with a rotating bombcalorimeter. Their result is in agreement with the resD fH°(298.15 K,cr)52(510.568.3) kJ mol21 of Smithet al.2 from their re-evaluation of earlier static bomb calrimetry 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 frKnudsen effusion experiments. This value is supportedapplication of Hess’s law where the enthalpy of sublimatis the sum of five processes at the standard pressure of 1Thus,
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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 valuof 144 J K21 mol21 over the range of 288–318 K reportedPickering4 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
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e,
483483NIST-JANAF THERMOCHEMICAL TABLES
Dow
TABLE 2. Ideal gas thermodynamic properties of chloroacetic acid C2H3ClO2(g) at the standard state pressurp°50.1 MPa~Tr5298.15 K!
is derived from vapor pressure data over a temperature rafrom 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 estimDsubH°(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,assume 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 a
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(CH2Cl—CO—OH) has thecis-synstructure~Cs symmetry!with the cis configuration for the carboxylic group and witthe chlorine atom lying in the carboxylic plane eclipsed wthe carbonyl group. The second more stable form cosponds 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 conformechloroacetic acid were determined by gas phase elecdiffraction.14 These parameters are in good agreement wresults fromab initio18,19 and molecular mechanics15 calcu-lations. In this work, the product of the principal momentsinertia for the most stablecis-synconformer of chloroaceticacid was calculated using rotational constants determifrom the microwave study.13 Structural parameters giveabove are those obtained from the electron diffract
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
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484484 DOROFEEVA, NOVIKOV, AND NEUMANN
study.14 These parameters reproduce the product of the pcipal moments of inertia calculated above within 3%.
Three conformations with respect to internal rotatiaround the C—C bond were found from an electron diffraction investigation,14 namely, 56% of acis-synconformation,30% of a cis-gaucheconformation with the CH2Cl grouprotated 131° from the former position, and the remain14% of acis-gaucheconformation with 79° rotation of theCH2Cl group. Three conformers of chloroacetic acid weidentified by vibrational spectroscopy.15–18 Two of themwere cis-synand cis-gauchein agreement with the electrodiffraction data. The third stable form was found to havetrans structure, in which the carboxylic hydrogen atom isthe 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 mechanicstudies15 strongly suggest that the third stable form shouldthe trans form. The barrier height for the rotation of the Ogroup around the C—O bond is predicted to be 1700–350cm21.16–18Due to the height of this barrier and the tempeture range of the present tabulation, this internal rotation wignored in this work.
Two cis conformers with respect to internal rotation abothe C—C bond were considered in this work: thecis-synconformer ofCs symmetry and two enantiomeric forms ocis-gaucheconformer ofC1 symmetry. The observed datand the calculations14,16–18 consistently predict a slight energy preference for thecis-synform and a small barrier o~400–450! cm21 for its interconversion. The simple potenti
V~w!5 12V3~12cos 3w!,
wherew is the Cl—C—CvO torsional angle, is used herfor a very approximate calculation of the internal rotationcontributions to the thermodynamic functions of chloroaceacid. The value of the reduced moment of inertia for tCH2Cl top was derived from the electron diffraction strutural parameters.14
Vibrational spectra of chloroacetic acid were studied inliquid and solid phases,15,20,21in the vapor22 and matrix.16,18
The fundamental frequencies adopted in this work are thderived 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 gooagreement 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 microwave spectrum13 and it coincides with the value calculated by theab initio method.18
The uncertainties in the calculated thermodynamic futions~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 vibrationalquencies and the approximate treatment of the internal rtion.
Thermodynamic properties of chloroacetic acid were cculated earlier by Banerjee23 using molecular constantknown at that time. A value for the barrier height of;1750
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-s
t
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cm21 was adopted for calculating the internal rotation cotributions of the CH2Cl and OH groups. The difference between 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 discrepain molecular constants used. The calculation of Banerje23
seems to be in error. The rough estimate by the methodgroup 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,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.7,483 ~2001!.
2L. Smith, L. Bjellerup, S. Krook, and H. Westermark, Acta Chem. Sca7, 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 Numb69, 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 Organometa
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. S
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. Wilho
Thermodynamics of Organic Compounds in the Gas State~Thermodynam-ics Research Center, College Station, TX, 1994!, Vol. I, p. 341.
ense or copyright; see http://jpcrd.aip.org/about/rights_and_permissions
485485NIST-JANAF THERMOCHEMICAL TABLES
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.
ob
.
ete,
ainvelt
ab-
rd
inlvi-as-f
ent
y-
nc-
4.1. Enthalpy of Formation
The recommended value of enthalpy of formation of oxpropanedinitrile is based on calorimetric measurementsvon Glemser and Ha¨usser1 as evaluated by Cox and Pilcher2
4.2. Heat Capacity and Entropy
Spectroscopic,3–10 electron diffraction,11 andtheoretical12–20 investigations have shown that oxopropandinitrile, CO~CN!2, is planar in its ground electronic staX 1A1 and belongs to theC2n symmetry group. In this workthe product of the principal moments of inertia of CO~CN!2
was calculated using the rotational constants determinedmicrowave spectroscopy.4 In the absence of isotopic data,unique set of geometrical parameters cannot be obtafrom the microwave spectrum. Structural parameters giabove arer e parameters determined by combining the resuof electron diffraction, microwave spectroscopy, andab ini-tio calculations.20 These parameters give values for rotationconstants which are only 0.3%–0.9% different from the oserved values. The C—C[N chain appears to be nearly lin
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-y
-
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ear, the deviation from linearity being 0.8°. A small inwabend ~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 studiedthe gas, liquid, and solid phase5–10 but there are still severauncertainties in the assignment of the fundamentals. Thebrational frequencies accepted in this work are thosesigned by Milleret al.9 from infrared and Raman spectra ogaseous and liquid oxopropanedinitrile. Their assignmwas 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 thermodnamic functions.
The uncertainties in the calculated thermodynamic futions ~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-
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
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fofnnoo
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M
486486 DOROFEEVA, NOVIKOV, AND NEUMANN
tion structural parameters11 and the vibrational assignment oBates and Smith.8 The numerical data in the four columnsthe table of thermodynamic functions in Natarajan aRajendran22 are transposed. Moreover, these functions docorrespond to the molecular constants used by the authThe 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 mlecular 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 Organometalic 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!.
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
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dt
rs.
-
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. Phys9,969 ~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: THEOCHE89, 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!.
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487487NIST-JANAF THERMOCHEMICAL TABLES
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
are
i-
th
5.1. Enthalpy of Formation
No experimental or theoretical data on enthalpy of formtion of gaseous glycolic acid are known from the literatuThe value accepted in this work,D fH° (298.15 K)52(583610) kJ mol21, is based on two estimates by addtivity methods.
The first value was estimated by group additivity usingequation
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!#
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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#
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489489NIST-JANAF THERMOCHEMICAL TABLES
5~221.8!1~218.8!
2~27.1!5233.5 kJ mol21.
The otherD fH° value of glycolic acid may be predicted bthe 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 toenthalpy 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 towathe carbonyl oxygen of carboxyl group. This structurevolves the intramolecular bonding between the alcoholdrogen and the carbonyl oxygen. With the exception ofmethylene hydrogen all the atoms in the molecule wfound to be coplanar. The pathways and energy barriersvolved in possible conformational interconversions of gcolic acid were investigated byab initio calculations.7–12
Along with rotamers ofcis-glycolic acid, where the carbonygroup has thecis conformation with its hydroxyl group, theconformers oftrans-glycolic acid were predicted from theoretical studies. Based on electron diffraction data13 the sec-ond lowest conformer has been assigned to acis-glycolicacid with hydrogen bonding between two hydroxyl groupThe energy difference between these conformers was foto be 1470 cm21 based on fitting to the diffraction dataHowever, this result is in conflict with theoretical data8,10–12
predicting the energy difference for the two lowest conforers to be 530–880 cm21. Moreover, it has been shown bGodfreyet al.11 from ab initio calculations and a microwavstudy that the two experimentally observed glycolic acid scies need not necessarily be the two of lowest energy.authors in Ref. 11 have assigned the second conformertected 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 conformof glycolic acid adopted in this work are based on thetailed ab initio calculations of Godfreyet al.11 who testedsome of their predictions experimentally. The lowest ene
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conformer identified byab initio calculation11 was found tobe theC1 conformer which is a slightly twisted version othe Cs from detected by microwave spectroscopy.4–6 A con-former of C1 symmetry exists in two enantiomeric formand 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 smetric double wells may be greater than the height ofsaddle point, in which case the effective structure of theserved conformer would closely match theCs conformer ofthe saddle point. It should be noted that the decision betwassigningCs or C1 symmetry is of great importance for thcalculation of the thermodynamic functions. ForC1 symme-try the termR ln 2 must be added to both the entropy aGibbs energy function because two optically isomeric forare present.C1 symmetry was accepted in this work as tpoint group of the lowest-energy form of glycolic acid.
The product of the principal moments of inertia for thmost stable conformer of glycolic acid was calculated usthe rotational constants determined from microwave sptrum investigation.4 Structural parameters given above wedetermined from the microwave spectra of normal and itopically substituted species of glycolic acid.5 In general,these geometric molecular parameters are close to thosetermined 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 tothe second lowest conformer with relative energy of 6cm21. In this work, the energy profile between two lowesenergy C1 conformers11 was approximated by a potentiaenergy 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 eighcoefficients (Vn) in the expansion for this moderately complex potential energy function were determined using dfrom 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 barrheight between its enantiomeric forms~1.5 cm21!, they arenot represented by the above potential and their contribuwas 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 fromsecondC1 stable conformer with an energy minimum of 69cm21 at f5155°. There is a barrier of 338 cm21 at w5180° between this conformer and its mirror image. Tvalue of the reduced moment of inertiaI r was calculatedusing the molecular structural parameters of Blom aBauder.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 intern
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thw-i
or-oropol.
th
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.
490490 DOROFEEVA, NOVIKOV, AND NEUMANN
rotation and adopting their molecular constants to besame as those of the basic conformer. The conformersenergies of about 2000 cm21 and higher were ignored because of their negligible contribution to the thermodynamfunctions.
Hollensteinet al.14 have measured the infrared spectra11 isotopic modifications of glycolic acid isolated in an agon matrix and have evaluated the transferable valence ffield that reproduced the observed frequencies and isotshifts very satisfactorily. The vibrational assignment by Hlensteinet al.14 for Cs symmetry is adopted in this workFundamentals of glycolic acid calculated by anab initiomethod10 are close to experimental values except forlow-frequency torsional mode.
The uncertainties in the calculated thermodynamic futions ~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 tthe approximate treatment of internal rotation in glycoacid.
Ideal gas thermodynamic properties of glycolic acid hanot been reported previously.
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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 Compounds~Thermodynamics Research Center, College Station, TX, 19!,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!.
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491491NIST-JANAF THERMOCHEMICAL TABLES
Dow
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
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493493NIST-JANAF THERMOCHEMICAL TABLES
6.1. Enthalpy of Formation
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.lower 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 diffracand rotational data.36 As trans-glyoxal has no dipole mo-ment, there is no microwave spectrum, and accurate rtional constants for the ground state can only be obtainedrotational analysis of infrared or electronic absorption banThe values obtained for the rotational constantstrans-glyoxal4,5,13,14,37 are in good agreement with eacother. Using the rotational constants for the five isotopic scies, Birsset al.11 have evaluated the structural parametfor trans-glyoxal. These parameters are in excellent agrment with electron diffraction results.36 In general, these experimental geometries are in good agreement with theoreresults.24,26,28,33–35,38–43The product of the principal moments of inertia for the planar structure oftrans-glyoxal ofC2h symmetry was calculated here using the rotational cstants determined from a high-resolution Fourier-transfostudy of trans-glyoxal.15 Structural parameters oftrans-glyoxal given above are those obtained from an electronfraction investigation.36 These parameters reproduce tspectroscopic moments of inertia with in an accuracy0.2%–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 usinthe rotational constants determined from microwastudies.17,18 Sets of possible structural parameters ofcis-glyoxal were evaluated using the rotational constants forisotopomers combined with assumptions of the valuessome 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 gphase4–8,10,13,15,16,45–55 and with matrix isolationtechniques.56–58 The experimental assignments have beconfirmed 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
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stretching band5 (n9) and a high-resolution infrared Fourietransform study15 (n10). The uncertainties in these values awithin 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 frequencies (n8 ,n9 ,n11,n12), the values were selected on the baof ab initio calculations;28,31,35,68and their uncertainties arestimated to be 25–50 cm21.
The torsional potential function for glyoxal has been ivestigated 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 potential 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 thcis and trans conformers has been revised upwards twiceButz 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 glyoxaby microwave spectroscopy. This value is intermediatetween the values reported by Butzet al.13,16 Based on thisvalue forDH, Hubneret al.18 have recalculated the potentiacurve 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 amongavailable experimental data.
The torsional potential function determined by Hu¨bneret al.18 is accepted in this work in order to account for thinternal rotation in glyoxal. The Fourier expansion coefcients 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 glyohave been identified with transitions to the excited eltronic states a 3Au (T0519 199 cm21) and A 1Au (T0
521 973 cm21).45,73,74 These assignments agree with othexperimental75–79 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, thare not considered in this work. These electronic stawould only make an appreciable contribution to the therm
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494494 DOROFEEVA, NOVIKOV, AND NEUMANN
J. Phys. Chem. Ref
Dow
TABLE 5. Ideal gas thermodynamic properties of glyoxal C2H2O2(g) at the standard state pressure,p°50.1 MPa~Tr5298.15 K)
dynamic functions at temperatures above 3000 K.The uncertainties in the calculated thermodynamic fu
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 equilibriumixture of trans and cis conformers were calculated bCompton.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 differ
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molecular constants used in the calculations and the noclusion of internal rotation in glyoxal by Compton.83 Valuesof H°(T)2H°(0) given by Compton appear to be in erroHollensteinet al.84 derived the thermodynamic functions oglyoxal using the semiclassical approximation for the suover-states calculation for nonrigid molecules. The diffeence between theirCp°(T) andS°(T) values and those calculated in this work range from 0.1 to 8.8 J K21 mol21
depending on the level of approximation used. The discrancies with the results of statistical calculations by Natara
ense or copyright; see http://jpcrd.aip.org/about/rights_and_permissions
em
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495495NIST-JANAF THERMOCHEMICAL TABLES
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. ChPhys.106, 1063~1997!.
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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. Gree
S. M. Japar, R. Nanes, B. J. Orr, D. A. Ramsay, and J. Szyszka, CaPhys.55, 390 ~1977!.
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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,
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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. P
125, 63 ~1988!.29G. E. Scuseria and H. F. Schaefer III, J. Am. Chem. Soc.111, 7761
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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. Ram
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. Chem99,
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. H
man, J. Mol. Spectrosc.149, 348 ~1991!.75W. Goetz, A. J. McHugh, and D. A. Ramsay, Can. J. Phys.48, 1 ~1970!.76L. G. Anderson, C. S. Parmenter, H. M. Poland, and J. D. Rau, Ch
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, Che
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. Phys67,
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 Ch
Soc.59, 1155~1982!.
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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.
ai
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7.1. Enthalpy of Formation
No experimental data are available for enthalpy of formtion of the cyanooxomethyl radical. The value acceptedthis work was estimated by Francisco and Liu1 by using theisodesmic reaction approach with the following reaction:
OCCN1HCN→C2N21HCO.
The relationship between the enthalpy of formationOCCN 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 formationHCN, C2N2, HCO, and theD rH° value predicted byab ini-tio calculations, Francisco and Liu1 have estimated the enthalpy 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 vibtional 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 calclated using the structural parameters shown above. Th
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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 constantCOX2 and XCO (X5F, Cl, Br). Normal coordinate analysifor CO~CN!2 was carried using the vibrational assignmentMiller et al.3 The uncertainties in the calculated frequencof OCCN can reach 50 cm21. These frequencies agree oveall 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 thwork. Structural parameters and vibrational frequenciesthe A 2A9 state were accepted as identical to those ofground state.
ense or copyright; see http://jpcrd.aip.org/about/rights_and_permissions
nc
m
497497NIST-JANAF THERMOCHEMICAL TABLES
The uncertainties in the calculated thermodynamic futions ~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 cyanooxoethyl radical have not been reported previously.
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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.
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8.1. Enthalpy of Formation
Wilhoit and Shiao1 have measured the enthalpy of combustion of solid oxalic acid in a rotating platinum bomb carimeter 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 vaby 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 aIR study of oxalic acid indicating that the structure was inplanar trans conformation ~C2h symmetry! in which the
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hydrogen atom of one COOH group participated in intramlecular hydrogen bonding with the carbonyl oxygen of tother 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 consion was made that a second conformer of oxalic acid exin the vapor phase. This conformer was suggested to btrans form ~C2h symmetry! with the hydrogen atom of eacCOOH group oriented towards the carbonyl oxygen ofsame COOH group~‘‘free’’ trans form!. Oxalic acid wasdetermined to be in itstrans conformation from x-ray crys-tallographic studies5 and no other conformers were observeStudies of oxalic acid in solution6 favored almost free rota
ense or copyright; see http://jpcrd.aip.org/about/rights_and_permissions
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499499NIST-JANAF THERMOCHEMICAL TABLES
tion, which would include a range of possible conformatioAb initio studies of oxalic acid7–9 have obtained a mosstable hydrogen bondedtrans planar structure in agreemenwith the results of an electron diffraction investigation.3 Thehydrogen bonded or freetrans form was found to be lowesenergy depending on the basis set used in theab initiocalculations.10 The freetrans conformer was reported to bmost 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 principmoments of inertia was calculated using the structuralrameters determined from the electron diffraction stud3
Following the results of a theoretical calculation by Tyrrel9
it was assumed that there is a slight energy preferencethis conformer and only a small barrier of about 2 kcal mo21
~700 cm21! separating it from other stable conformers. Tsimple approximate potential,
V~w!5 12V1~12cosw!,
wherew is the OC—CO torsional angle, was used here fthe calculation of internal rotational contributions to the thmodynamic functions of oxalic acid. The value of the rduced moment of inertia for the COOH top was derived frothe molecular constants shown above.
There are several studies of the vibrational spectra offree C2H2O4 molecule3,4,12–14but some fundamentals are stunobserved. Stace and Oralratmanee14 have reported the infrared vapor phase measurements and the first vapor pRaman spectra. They have proposed a new vibrationalquencies assignment based on their experimental resulwell as calculated in-plane frequencies using an UreBradley force field derived from formic and acetic acid. Reington and Redington4 have investigated the infrared spectof oxalic acid vapor and the infrared spectra of matrisolated C2H2O4, C2HDO4, and C2D2O4 and have carried oua normal coordinate analysis using a general valence ffield for the in-plane infrared-active modes. None of tabove studies, however, gives a complete vibrational assment for oxalic acid. De Villepin and Novak15 have devel-oped a general valence force field for both infrared andman frequencies using the relatively small numberexperimentally observed fundamentals. Their force fieldproduces the experimental vibrational spectra of oxalicis comparable with force fields already known for other cboxylic acids. The fundamental frequenciesn22n5 and n7
adopted here were observed in the Raman spectra of gasoxalic acid.14 The 405 cm21 mode was subsequently reasigned 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-isolatoxalic acid.4 The uncertainties in these experimental frequcies are in the range of 5–10 cm21.
Redington and Redington4 have suggested tentative valufor n6(Ag)5538 cm21, n11(Bg)5590 cm21, and n12(Bg)5512 cm21 fundamentals using possible combination ban
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The adopted values of these frequencies were taken fnormal coordinate calculations.15 Calculations for the otherfrequencies are in good agreement with experimental resThe value of the symmetric O—H stretching frequencyn1
was accepted to be the same as the value of antisymmO—H stretching (n13) and it coincides with the calculatevalue.15 The uncertainties in these frequencies are estimato be 25–50 cm21.
Evidently due to its weak intensity, the C—C torsionmode n10(Au) was not observed in a vapor phase specsearch 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 otcalculated values are much greater than those from expment. Cyvin and Alfheim16 have calculatedn10590 cm21
using force constants transferred from formic and aceticids. The value of 110 cm21 was obtained from other normacoordinate calculation.15 The corresponding torsional modfor 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 futions ~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 ofvibrational frequencies and the simple and approximmodel for internal rotation.
Ideal gas thermodynamic properties of oxalic achave 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. CrystolCryst. 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!.
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500500 DOROFEEVA, NOVIKOV, AND NEUMANN
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.
ailf
de
nt
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i-
9.1. Enthalpy of Formation
Experimental data on enthalpy of formation are not avable for methyl hydroperoxide. Values oD 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 determinevalue ofD fH°(CH3OO) with an average bond energy for thO–H bond in ROOH compounds. Based on the experimevalues 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 mthyl 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
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al
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 est
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502502 DOROFEEVA, NOVIKOV, AND NEUMANN
mates,213965.0 kJ mol21, is accepted in this work for theenthalpy of formation of methyl hydroperoxide at 298.15
9.2. Heat Capacity and Entropy
The microwave spectrum of methyl hydroperoxidCH3OOH, has been investigated by Tyblewskiet al.16 How-ever, the assignment of the spectrum was complicatedcause of the widespread effects of the internal rotataround the O—O bond. The experimental results providdefinitive evidence that the minimum of the potential enerelative to internal rotation around the O—O bond corre-sponds to askewconformation. The adjustment to the oserved data resulted in a smalltrans barrier of 172.5 cm21.This barrier separates two equivalent potential minima asciated 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 d/C—C—O5105.3°. All other structural parameters weadopted by those authors fromab initio calculations. Confor-mational properties of methyl hydroperoxide have beenvestigated theoretically.1,2,4–6,11,16,18–22Ab initio5,16,19–22andmolecular mechanics4,6 calculations provide an equilibriummolecular structure andtransbarrier in close agreement witthe conclusions of experimental study of Tyblewskiet al.16
The product of the principal moments of inertia of methhydroperoxide was calculated in this work using the rotional constants determined from a microwave study16
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 diby 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 rotwere evaluated in this work based on available data on rtional barriers in CH3OOH. The value ofV351120 cm21
was accepted for the barrier to internal rotation of the metgroup around the C—O bond. This value was found from thmicrowave study16 and agrees closely with values obtainfrom ab initio calculations.4,16 The double-minimum potential 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 pottial function in hydrogen peroxide.24 The expansion coeffi-cientsV0 , V1 , V2 , andV3 can be expressed in terms of thtrans barrier heightVtrans , the cis barrier heightVcis , andthe COOH dihedral anglewe corresponding to a minimum othe 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
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5172.5 cm21(/C—O—O—H5180°) was taken from themicrowave study.16 It should be noted that substantiallower 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. Ivalue accepted in this work is based on theoretiresults4–6,16,25which agree closely with each other. The equlibrium COOH dihedral angle,we5120°, was estimated inthis work ~see above!. The values of the reduced momentsinertia for CH3 and OH tops were calculated from structurparameters given above.
Experimental data on the vibrational spectra of methyl hdroperoxide are unknown. Vibrational frequenciesCH3OOH were predicted fromab initio calculations.16,22 Inthis work, fundamental frequencies of methyl hydroperoxwere estimated by normal coordinate calculations using foconstants 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 areunits of mdyn/Å; bend and torsion constants are in unitsmdyn Å; stretch-bend interaction constants are in unitsmdyn!. The valence force fields for CH3OOCH3 and H2O2
were obtained from normal coordinate calculations usknown vibrational assignments.6,26 Comparison of our fre-quencies with those obtained inab initio calculations16,22
shows satisfactory agreement taking into account thethat theab initio frequencies are unscaled and the anharmnicity contributions are neglected.
The uncertainties in the calculated thermodynamic futions ~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 uncetainties in the adopted vibrational frequencies and theproximate model used for internal rotation.
Ideal gas thermodynamic properties of methyl hydropoxide 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, GM. 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!.
ense or copyright; see http://jpcrd.aip.org/about/rights_and_permissions
V.
m-94
o
m.
o-
ys.
503503NIST-JANAF THERMOCHEMICAL TABLES
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.
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 Co
pounds~Thermodynamics Research Center, College Station, TX, 19!,Vol. I.
15G. Baker, J. H. Littlefair, R. Shaw, and J. C. J. Thynne, J. Chem. S6970 ~1965!.
16M. Tyblewski, T. K. Ha, R. Meyer, A. Bauder, and C. E. Blom, J. ChePhys.97, 6168~1992!.
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c.
17M. Tyblewski, R. Meyer, and A. Bauder, 8th Colloquium on High Reslution 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. Ph
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!.
e,
TABLE 8. Ideal gas thermodynamic properties of methyl hydroperoxide CH4O2~g! at the standard state pressurp°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.
-
fof
10.1. Enthalpy of Formation
The enthalpy of formation of dimethyl peroxide recommended in this work~2125.5 kJ mol21! was de-termined by Bakeret al.1 from calorimetric measurements othe enthalpy of combustion. Slightly lower values
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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
ense or copyright; see http://jpcrd.aip.org/about/rights_and_permissions
-
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505505NIST-JANAF THERMOCHEMICAL TABLES
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 approaches. Semiempirical MINDO9,10 and molecularmechanics11 calculations provideD fH° ~298.15 K! values,2105.1 to2121.6 kJ mol21, which are greater than the experimental value. The available theoretical and empirievaluations are grounds to believe that the experimevalue of D fH° ~298.15 K! may be overestimated. Thus, iuncertainty was increased in this work.
10.2. Heat Capacity and Entropy
The molecular structure of dimethyl peroxidCH3OOCH3, was studied by electron diffraction.12 The mo-lecular intensities were analyzed using a model which csidered 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 spectinvestigations20,21 andab initio calculations8,22–24support anexactly planar or nearly planartransconfiguration. However,it should be noted that the value of a dihedral angle depestrongly on the basis set and method used.19 Hamada andMorishita25 have described the Raman and infrared speof CH3OOCH3 in terms of planar structure ofD3h symmetry.In this work, the product of the principal moments of inerof dimethyl peroxide forskewconformation ofC2 symmetrywas calculated using the structural parameters determfrom electron diffraction study.12
The dimethyl peroxide molecule undergoes three laramplitude 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 thermodynamproperties from these hindered rotors were calculated inwork based on available data on the rotational barriersCH3OOCH3. The value ofV35900 cm21 was accepted forthe internal rotation barrier of methyl groups around the Cbonds. This value was used by Koput26 in his theoreticalmodel describing the internal rotation in dimethyl peroxiand it is the average of the results of molecular mechacalculations.4 The double-minimum potential energy funtion,
V~w!5V01V1 cosw1V2 cos 2w1V3 cos 3w,
was used in this work for the internal rotation around tO—O bond. This function was chosen earlier for the hdered rotation potential function in hydrogen peroxide.27 Theexpansion coefficientsV0 , V1 , V2 , andV3 can be expresse
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lal
-
ds
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-
isin
s
-
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 assuminVtrans587 cm21, Vcis54700 cm21, and we5119°. Thevalue of Vtrans was taken from the electron diffractiostudy.12 It agrees with results of theoretical calculations4,5,8,19
within the limits of experimental accuracy. The adoptvalue ofVcis is based on results ofab initio8,18and molecularmechanics4,5 calculations. The values of the reduced mments of inertia for CH3 and OCH3 tops were calculatedfrom structural parameters given above.
Christe13 has investigated the infrared spectraCH3OOCH3 and CD3OOCD3 both in the gas phase and in aAr matrix and the Raman spectra of these molecules inliquid phase. The vibrational assignment proposedChriste13 has considerable uncertainty for a number of tvibrations, and the low-frequency modes were not assigat all. Bell and Laane14 have carried out a normal coordinaanalysis of dimethyl peroxide using the experimental dataChriste.13 Hamada and Morishita25 have described the vibrational spectra of CH3OOCH3 in terms of D3h symmetry.However, this assignment is in conflict with available infomation on dimethyl peroxide. There are twoab initio calcu-lations of vibrational frequencies of CH3OOCH3.
23,28Resultsof Benassi and Taddei23 show overall agreement with expermental data taking into account the fact that theab initiofrequencies are unscaled and the anharmonicity contributare neglected. Chen and Allinger5 have carried out the molecular mechanics calculation of vibrational frequenciesdimethyl peroxide. Their results are in agreement withavailable, but somewhat tentative and incomplete, expmental data.13 The assignment proposed by Chen aAllinger5 is accepted in this work.
The uncertainties in the calculated thermodynamic futions ~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 uncertainties in the adopted vibrational frequencies and the apprmate treatment of internal rotation.
Ideal gas thermodynamic properties of dimethyl peroxhave not been reported previously.
10.3. References
1G. Baker, J. H. Littlefair, R. Shaw, and J. C. J. Thynne, J. Chem. S6970 ~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!.
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
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.
r.
oc ys.
k.
506506 DOROFEEVA, NOVIKOV, AND NEUMANN
10V. N. Kokorev, N. N. Vyshinskii, V. P. Maslennikov, I. A. Abronin, GM. 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, Teo
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. S
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!.
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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. Ph
42, 1931~1965!.28G. A. Pitsevich, V. I. Gogolinskii, and I. P. Zyatkov, Zh. Prikl. Spektros
56, 643 ~1992!.
e,
TABLE 9. Ideal gas thermodynamic properties of dimethyl peroxide C2H6O2~g! at the standard state pressurp°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.
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
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508508 DOROFEEVA, NOVIKOV, AND NEUMANN
11.1. Enthalpy of Formation
Jaffeet al.1 determined the enthalpy of formation for liquid diacetyl peroxide (CH3CO—OO—COCH3) from calori-metric measurements. Assuming the enthalpy of vaporizaof diacetyl peroxide to be equal to the enthalpy of vaporition of acetic anhydride (CH3CO—O—COCH3), the authorsobtained the value of2498 kJ mol21 for the enthalpy offormation of gaseous diacetyl peroxide. A similar valueD fH°(298.15 K)52502 kJ mol21 may be derived from thegroup additivity contributions for peroxyacids and peroxyeters obtained by Benassi and Taddei2 using empirical ap-proaches andab initio calculations. The value predicted bthe 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 frthe compilation by Pedley3!, agrees with the two above estmates within the limits of the combined errors of those dterminations. Considerably lower values ofD fH° for di-acetyl peroxide were estimated from a group additivapproximation~2540 kJ mol21!4 and a semiempirical calculation ~;2585 kJ mol21!.5,6 The value recommended in thwork, 2(500610) kJ mol21, is based on the estimates.1,2
11.2. Heat Capacity and Entropy
Experimental data on molecular structure and vibratiofrequencies 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. Athough a planar structure was suggested for the peroxygroup in peroxyacetic acid from a microwave study,7 theskewconformation ofC2 symmetry is accepted in this worfor diacetyl peroxide in accord with a semiempiriccalculation5 and by analogy with dimethyl peroxide.8 Theproduct of the principal moments of inertia was calcula
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d
from structural parameters estimated by comparison wstructural parameters of CH3CO—OOH,7
CH3CO—O—COCH3,9 and CH3OOCH3.
8
The diacetyl peroxide molecule undergoes five largamplitude 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 rotatof CH3 groups were calculated in this work assuming theV3
barrier height to be the same as that in peroxyacetic ac7
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 pottial function in hydrogen peroxide.10 The expansion coeffi-cientsV0 , V1 , V2 , andV3 can be expressed in terms of thtrans barrier heightVtrans , the cis barrier heightVcis , andthe COOC dihedral anglewe corresponding to a minimum othe 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 overestimathe Vtrans and underestimated theVcis barriers for theCH3OOH and CH3OOCH3 molecules. The values of the reduced moments of inertia for CH3 and CH3COO tops werecalculated from structural parameters given above. Thereno 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 torsionmotion about the C-O bonds.
Zyatkovet al.11 have calculated vibrational frequenciesdiacetyl peroxide using a theoretical simulation of the forfield. In this work, vibrational frequencies oCH3CO—OO—COCH3 were calculated using force constants transferred from the CH3CO—OOH molecule. Thesimplified valence force field for that molecule was obtainby normal coordinate calculations for the vibrational assigment of Cugleyet al.12 The calculated force constants reprduce the observed vibrational wave numbersCH3CO—OOH with a root mean square deviation of 0cm21. The following 18 force constants were used for calclating 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
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509509NIST-JANAF THERMOCHEMICAL TABLES
~stretching and stretch-stretch interaction constants arunits of mdyn/Å; bending, wagging, and torsion constaare in units of mdyn Å; stretch-bend interaction constantsin units of mdyn!.
The uncertainties in the calculated thermodynamic futions ~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 thuncertainties in the adopted vibrational frequencies andapproximate treatment of internal rotation.
Ideal gas thermodynamic properties of diacetyl peroxhave 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!.
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insre
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e
e
3J. B. Pedley,Thermochemical Data and Structures of Organic Compounds~Thermodynamics Research Center, College Station, TX, 19!,Vol. I.
4S. W. Benson, F. R. Cruickshank, D. M. Golden, G. R. Haugen, H.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, GM. 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. Stru7, 421 ~1971!.
10R. H. Hunt, R. A. Leacock, C. W. Peters, and K. T. Hecht, J. Chem. Ph42, 1931~1965!.
11I. P. Zyatkov, V. I. Gogolinskii, V. V. Sivchik, and D. I. Sagaidak, ZhPrikl. Spektrosk.29, 652 ~1978!.
12J. A. Cugley, R. Meyer, and H. H. Gu¨nthard, Chem. Phys.18, 281~1976!.
e,
TABLE 10. Ideal gas thermodynamic properties of diacetyl peroxide, C4H6O4~g! at the standard state pressurp°50.1 MPa (Tr5298.15 K)
The thermodynamic properties of 10 organic molecuhave been calculated, based on the critical evaluationavailable thermodynamic and spectroscopic informatiWhere no data were available, estimation techniques wused. Recommended values for the entropy, heat capaand the enthalpy of formation at 298.15 K are summarizeTable 11.
For a first round of new experimental studies, substantiimproved formation properties could be obtained with nor confirming measurements for the enthalpy of formatfor bromoacetic acid, glycolic acid, the cyanooxomethradical, and the three peroxides—methyl hydroperoxidimethyl peroxide, and diacetyl peroxide. In order to calclate significantly more reliable thermal functions, the struture and the vibrational frequencies are needed for thenooxomethyl radical and diacetyl peroxide, since these dwere estimated for these two compounds.
. Data, Vol. 30, No. 2, 2001
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sof.reity,in
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nl,--a-ta
13. Acknowledgments
The authors wish to acknowledge the support of this wby the Upper Atmospheric Research Program of the NatioAeronautics 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 MarylanBaltimore County, for bringing to their attention the juspublished work, so relevant to this article, of the 10 scientof Portugal and Germany working with Professor ManuelMinas 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 ProfesVladimir Yungman of the Institute for High Temperature~IVTAN ! of the Russian Academy of Sciences, Dr. MalcoW. Chase of SRD, and Dr. Eugene S. Domalski of NISwhose expert advice, support, and encouragement weresential to the completion of this project.
ove but
rium
tional
hane,. Ther-
ics of
-
14. Extended Bibliographies
The following bibliography lists articles that were found in the literature pertaining to the molecules discussed abwere 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 equilibCH3COCH31Br25CH3COCH21HBr,’’ 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 rotaisomers 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 iodometdiiodomethane, triiodomethane, and tetraiodomethane by rotating combustion calorimetry,’’ J. Chemmodyn.25, 261–269~1993!.
14.2. Extended Bibliography for Chloroacetic Acid, C 2H3ClO2
64JOH Johansen, H., ‘‘Normal coordinate analysis of polyatomic molecules and statistical thermodynamisotopic molecules,’’ Z. Phys. Chem.227, 305–328~1964!.
75CHA/DEV Chandramani, R., Devaraj, N., ‘‘Torsional-vibration frequency ina-CH2ClCOOH and its temperature dependence 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!.
ense or copyright; see http://jpcrd.aip.org/about/rights_and_permissions
l
loro-
n J.
pec-
some
mistry
f theexcited
:
ogen
ctron
Soc.
2971
rbonyl
. J.,r 11
truct.
pe
th-
511511NIST-JANAF THERMOCHEMICAL TABLES
86FAU/TEI2 Fausto, R., Teixeira-Dias, J. J. C., ‘‘Conformational and vibrational spectroscopic analysis of CHC2COXand 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 dichacetic 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,’’ India
Pure Appl. Phys.8, 840–841~1970!.71DUN/WHI Duncan, A. B. F., Whitlock, R. F., ‘‘Vacuum ultraviolet absorption spectrum of carbonyl cyanide,’’ S
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
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 thermoche
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 oclassical notion of molecular structures: The cases of some small carbonyls in the ground andstates,’’ 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 compoundsglyoxal, 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-halcompounds 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 elediffraction 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.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–~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 ca
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
Ramsay, D. A., Roncin, J. Y.,‘‘The 4550 Å band system of glyoxal. III. Vibration-rotational analyses fobands 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. S18, 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 tymolecules by infinite matrix technique,’’ Chem. Phys.8, 252–271~1975!.
75PAN Pancir, J., ‘‘Cis-transisomerization of glyoxal. A contribution to the rehabilitation of semiempirical meods,’’ 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!.
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
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Chem.
a,’’
triplet
cular
level
oxal:
nyl
n ofetry,’’
mol-
oxal
s.
tra of
nal
ations
.
lysis,’’
charge
.
aining
. Phys.
512512 DOROFEEVA, NOVIKOV, AND NEUMANN
76DEV/TOW Devaquet, A. J. P., Townshend, R. E., Hehre, W. J., ‘‘Conformational studies of 1,3-dienes,’’ J. Am.Soc.98, 4068–4076~1976!.
77VON Von Niessen, W., ‘‘Trans- andcis-glyoxal: A Green’s function calculation on their photoelectron spectrJ. 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
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 mole
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
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 glyHCO—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 carbocompounds,’’ Chem. Phys.68, 143–154~1982!.
83PAN/MOC Panchenko, Y. N., Mochalov, V. I., Pentin, Y. A., ‘‘Calculation of potential curves of the internal rotatioglyoxal and its fluoro derivatives in the CNDO/2 approximation taking into account a change in geomVestn. 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 inecules 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 glyvapor,’’ 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. Phy85,3229–3236~1986!.
87PEB/JOS Pebay Peyroula, E., Jost, R., ‘‘S1←S0 laser excitation spectra of glyoxal in a supersonic jet: Vibratioanalysis,’’ 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 conformin conjugated molecules,’’ J. Comput. Chem.9, 369–377~1988!.
89BRI Brinn, I. M., ‘‘Fundamental vibrational frequency correlation. IV.C2v2C2h in-plane trends,’’ SpectrochimActa A 45, 653–659~1989!.
89MOH/PAY Mohan, S., Payami, F., Kuttiappan, P., ‘‘Laser Raman spectrum of glyoxal and its vibrational anaProc. 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,distributions, 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 Chem56, 19–26~1995!.
96PRO/SHO Promyslov, V. M., Shorygin, P. P., ‘‘Quantum-chemical study of conjugation in molecules contconjugated 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,’’ ChemLett. 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.
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
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with
h
cessive
f the
ylation
hys.
es of
les by
ol to
et.
on33–37
es in
ular
me
ave
related
513513NIST-JANAF THERMOCHEMICAL TABLES
92DOR/GUR Dorofeeva, O. V., Gurvich, L. V., ‘‘Thermodynamic properties of linear carbon chain moleculesconjugated 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 ResearcCenter, 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 sucterms 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 oa-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 decarboxand 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,’’ GeopRes. Lett.6, 953–955~1979!.
96GRE/COL Grela, M. A., Colussi, A. J., ‘‘Quantitative structure-stability relationships for oxides and peroxidpotential 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 molecuab 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 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. Kin14, 933–944~1982!.
92ZYA/KNY Zyatkov, I. P., Knyazhevich, N. D., Gogolinskii, V. I., Pitsevich, G. A., ‘‘Quantum-chemical calculationsstructure and conformations of organosilicon peroxides,’’ Vestn. Beloruss. Gos. Univ., Ser. 1, No. 2,~1992!.
96LEE/SHI Lee, S.-Y., Shin, Y.-J., ‘‘Estimation of thermodynamic properties in the pyrolysis of dialkyl peroxidhelium 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 molecstructure 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 schefor 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: Microwspectra, 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 structurallyradicals: 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!.
J. Phys. Chem. Ref. Data, Vol. 30, No. 2, 2001
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