CHAPTER –VII AB INITIO, DENSITY FUNCTIONAL THEORY AND …shodhganga.inflibnet.ac.in/bitstream/10603/4299/15/15... · 2015-12-04 · CHAPTER –VII AB INITIO, DENSITY FUNCTIONAL

CHAPTER –VII

AB INITIO, DENSITY FUNCTIONAL THEORY AND

STRUCTURAL STUDIES OF

4–AMINO–2–METHYLQUINOLINE

7.1. Introduction

Quinoline derivatives are biologically and pharmaceutically important

compounds. The 2–(aryl) quinolin–4–amine is used as inhibitors of human immuno

deficiency virus (HIV) [1]. Quinoline and their derivatives have been extensively

explored for their applications in the field of biological [2–5], anti filarial [6], anti

bacterial [7,8], anti malarial activities [9–14]. Quinolium derivatives have been

widely used as novel inhibitors. i.e., DHA topoisomerase II inhibitor [15],

topoisomerase inhibitor [16], lipoxygenase inhibitor [17], kinase inhibitor [18]. The

derivatives of quinoline are also extensively used as receptor agonists [19–23].

Cardiovascular [24] and anti neoplastic [25] activities of quinoline derivatives have

also been studied. Quinoline dyes are present in photographic sensitizers [26].

Quinoline yellow is used as textile dye for wool, nylon, silk and also for dying paper.

Printing ink contains quinoline yellow barium salt. Quinoline derivatives are

promising antiphlogistic activity in rats [27]. Pyrrolizidinylalkyl derivatives of

4–amino–7–chloroquinoline exhibited excellent antimalarial activity [28].

Aminoxazole, the 4–aminoquinoline have found potent antiplasmodial activity [29].

Chloroquine, a 4–aminoquinoline, accumulates in acidic digestive vacuoles of the

malaria parasite, preventing conversion of toxic haematin to β–haematin [30]. The

8–aminoquinoline family of drugs namely, primaquine, tafenoquine and pamaquine

[31] are used in the treatment of malaria. They may be used to eradicate malaria

hypnozoites from the liver and have both been used for malaria prophylaxis.

4–Aminoquinoline is most useful in treating erythrocytic plasmodial infections,

includes amodiaquine [32].

Ab initio calculations (HF and B3LYP) were performed on 2–aminoquinoline

[33], isoquinoline and 8–hydroxyquinoline [34], 8–hydroxyquinoline N–oxide [35]

237

and 2–, 4– and 6–methylquinoline [36]. The geometry and the complexing ability of

3–aminoquinoline and 8–aminoquinoline are investigated by infrared spectrometry in

carbon tetrachloride solution by Leroux et al. [37]. Ab initio calculations on 2–, 3–

and 4– substituted quinoline are carried out in a search for a relationship between the

molecular properties of these compounds and their activity as synthetic protein

tyrosine kinase inhibitors (tyrphostins) [38]. Ab initio study of luminescent

substituted 8–hydroxyquinoline metal complexes with application in organic light

emitting diodes was carried out by Zarur et al. [39].

The theoretical ab initio and normal coordinate analysis give information

regarding the nature of structure, the functional groups, orbital interactions and

mixing of skeletal frequencies. The introduction of one or more substituents in

quinoline ring leads to the variation of charge distribution in the molecule, and

consequently, this greatly affects the structural, electronic and vibrational parameters.

Though there are few studies on quinoline compounds [33–47], the structural

characteristics and vibrational spectroscopic analysis of 4–amino–2–methylquinoline

(AMQ) by the quantum mechanical ab initio and DFT methods have not been studied.

Thus, considering the industrial and biological importance of 4–amino–2–

methylquinoline, an extensive experimental and theoretical ab initio studies on AMQ

to obtain a complete reliable and accurate vibrational assignments and structural

characteristics of the compound. The density functional theory (DFT) is a popular

post–HF approach for the calculation of molecular structures, vibrational frequencies

and energies of molecules [48,49]. The DFT calculations with the hybrid exchange–

correlation functional B3LYP (Becke’s three parameter (B3) exchange in conjunction

with the Lee–Yang–Parr’s (LYP) correlation functional) which are especially

important in systems containing extensive electron conjugation and/or electron lone

pairs [50–55].

7.2. Experimental

The compound 4–amino–2–methylquinoline (AMQ) was obtained from

Aldrich chemicals, U.S.A and used as such to record FTIR and FT–Raman spectra.

The FTIR spectrum has been recorded by KBr disc method in the region between

4000 and 400 cm–1

using Bruker IFS 66V spectrometer. The frequencies for all sharp

bands are accurate to ±1 cm–1

. The FT–Raman spectrum was also recorded in the

238

range between 3500 to 100 cm–1

by the same instrument with FRA 106 Raman

module equipped with Nd:YAG laser source with 200 mW power operating at 1.064

µm and the spectral resolution is ±2 cm–1

.

7.3. Computational details

The combination of vibrational spectroscopy with ab initio calculations is

considered to be a powerful tool for understanding the fundamental mode of

vibrations of the compound. The structural characteristics, stability, thermodynamic

properties and energy of AMQ are determined by LCAO–MO–SCF restricted

Hartree–Fock (HF) and the gradient corrected density functional theory (DFT) [55]

with the three–parameter hybrid functional (B3) [51] for the exchange part and the

Lee–Yang–Parr (LYP) correlation function [52], using 6–31G** and 6–311++G**

basis sets with Gaussian–03 [56] program package, invoking gradient geometry

optimisation [57] on a Intel Core i5/3.03 GHz. To satisfactorily describe the

conformation and orientation of the amino and methyl groups, a fully polarized

6–31G** and 6–311++G** basis sets are required and considered to be a complete

basis sets. The energy minima with respect to the nuclear coordinates were obtained

by the simultaneous relaxation of all the geometric parameters using the gradient

methods and the initial geometry generated from standard geometrical parameters was

minimised without any constraint in the potential energy surface at Hartree–Fock

level, adopting the 6–31G** and 6–311++G** basis sets. The optimised structural

parameters were used in the vibrational frequency calculations at the HF and DFT

levels to characterise all stationary points as minima.

The force constants obtained from the ab initio basis sets have been utilised in

the normal coordinate analysis by Wilson’s FG matrix method [58–60]. The potential

energy distribution corresponding to each of the observed frequencies were calculated

with the program of Fuhrer et al. [61]. The force constants were refined by damped

least square technique to achieve a close agreement between the observed and

calculated frequencies.

239

7.4. Results and discussion

7.4.1. Structural properties

The structure and the scheme of numbering the atoms of 4–amino–2–

methylquinoline is shown in Figure 7.1. The optimised structural parameters bond

length and bond angle for the thermodynamically preferred geometry of AMQ

determined at HF/6–31G**, B3LYP/6–31G**, HF/6–311++G** and B3LYP/

6–311++G** levels are presented in Table 7.1 in accordance with the atom

numbering scheme of the molecule shown in Figure 7.1.

C6

C7

C8

C10

C9

C5

N1

C2

C3

C4

H14 N12

H13

C11H16

H15

H17

H20

H18

H19

H21 H22

Figure 7.1. Structure and atom numbering scheme of 4–amino–2–methylquinoline

240

From the structural data given in Table 7.1 it is observed that the various C–C

bond distances calculated between the ring carbon atoms and the C–H bond length are

found to be the same at all levels of calculations. The bond lengths determined from

B3LYP method are slightly higher than that obtained from HF method but it yields

bond angles in excellent agreement with the HF method. The influence of the

substituent on the molecular parameters, particularly in the C–C bond distance of ring

carbon atoms seems to be small except that C4–C9 bond length is longer than others,

where the amino group is attached with C4. The shorter the bond length of C4–N12

indicates that the benzene ring exerts larger attraction on valance electron cloud of

nitrogen atom resulting easy delocalisation of lone pair of electrons in to the ring and

there by increase in force constant and decrease in bond length. The calculated bond

angles are very close to each other except for the CCC bond angle at the point of

amino and methyl group substitution. With the electron donating substituents on the

benzene ring, the symmetry of the ring is distorted, yielding ring angles smaller than

120o at the point of substitution and slightly larger than 120

o at the ortho and meta

positions [62]. Similar trend is observed in AMQ molecule where the bond angle C3–

C4–C9 is around 117.8o while at ortho, N1–C2–C3 and meta, C2–C3–C4 positions

the angles are found to be around 123.2 and 120.0 degree, respectively. Introduction

of nitrogen atom leads to significant perturbations in the hetero substituted ring of

quinoline moiety, although the geometry of the benzene ring is seen to be relatively

unperturbed. The thermodynamic parameters of the compound have also been

computed at ab initio HF/6–31G**, B3LYP/6–31G**, HF/6–311++G** and

B3LYP/6–311++G** methods are presented in Table 7.2. The total thermal energy,

vibrational energy contribution to the total energy, the rotational constants and the

dipole moment values obtained from HF method are slightly over estimated than that

of DFT/B3LYP method. From Table 7.2 it is observed that the dipole moments of

AMQ calculated at HF and B3LYP methods are higher than the dipole moments of

quinoline [63] and is due to the presence of amino and methyl groups.

The geometry of the molecules under investigation is considered by

possessing CS point group symmetry. The symmetry coordinates of AMQ are given

in Table 7.3. The 60 fundamental modes of vibrations of the compound are

distributed into the irreducible representations under CS symmetry as 40 in–plane

241

vibrations of A′ species and 20 out of plane vibrations of A″ species. i.e., Γvib = 40A′

+ 20A″. All vibrations are active in both IR and Raman. All the frequencies are

assigned in terms of fundamental, overtone and combination bands.

7.4.2. Analysis of Molecular electrostatic potential (MESP)

The molecular electrostatic potential surface (MESP) which is mapping

electrostatic potential onto the iso–electron density surface simultaneously displays

electrostatic potential (electron + nuclei) distribution, molecular shape, size and dipole

moments of the molecule and it provides a visual method to understand the relative

polarity of the compounds. Electrostatic potential maps illustrate the charge

distributions of molecules three dimensionally. These maps allow us to visualise

variably charged regions of a molecule. Knowledge of the charge distributions can be

used to determine how molecules interact with one another. One of the purposes of

finding the electrostatic potential is to find the reactive site of a molecule. In the

electrostatic potential map, the semi–spherical blue shapes that emerge from the edges

of the above electrostatic potential map are hydrogen atoms. The molecular

electrostatic potential (MEP) at a point r in the space around a molecule (in atomic

units) can be expressed as:

∫∑ →→

→

→→

−

−

−

=

rr

drr

rR

ZrV

A

A

A

'

')'()(

ρ

where, ZA is the charge on nucleus A, located at RA and ρ(r′) is the electronic density

function for the molecule. The first and second terms represent the contributions to

the potential due to nuclei and electrons, respectively. V(r) is the resultant at each

point r, which is the net electrostatic effect produced at the point r by both the

electrons and nuclei of the molecule

The total electron density and MESP surfaces of the molecules under

investigation are constructed by using B3LYP/6–311++G** method. These pictures

illustrate an electrostatic potential model of the compounds, computed at the 0.002 au

isodensity surface. The MESP mapped surface of the compounds and electrostatic

potential contour map for positive and negative potentials are shown in Figures 7.2

and 7.4. The colour scheme of MESP is the negative electrostatic potentials are shown

in red, the intensity of which is proportional to the absolute value of the potential

242

energy, and positive electrostatic potentials are shown in blue while Green indicates

surface areas where the potentials are close to zero. The colour–coded values are then

projected onto the 0.002 au isodensity surface to produce a three–

dimensional electrostatic potential model. Local negative electrostatic potentials (red)

signal nitrogen atoms with lone pairs whereas local positive electrostatic potentials

(blue) signal polar hydrogens in N–H bonds. Green areas cover parts of the molecule

where electrostatic potentials are close to zero (C–C and C–H bonds). The

electrostatic potential mapped surfaces of the compounds are shown in Figure 7.4.

Figure 7.2. The total electron density isosurface mapped with molecular electrostatic

potential of 4–amino–2–methylquinoline

243

Figure 7.3. The contour map of molecular electrostatic potential surface of

4–amino–2–methylquinoline

Figure 7.4. Electrostatic potential surface of 4–amino–2–methylquinoline

244

7.5. Vibrational analysis

The observed and theoretical FTIR and FT–Raman spectra of AMQ are given

in Figures 7.5 and 7.6. The observed and calculated frequencies using ab initio HF/

6–31G**, B3LYP/6–31G** and HF/6–311++G**, B3LYP/6–311++G** force field

along with their relative intensities, probable assignments and potential energy

distribution (PED) of AMQ are summerised in Tables 7.4 and 7.5, respectively.

Figure 7.5. FTIR spectrum of 4–amino–2–methylquinoline (a) Observed

(b)Theoretical HF/6–311++G** and (c) B3LYP/6–311++G**

245

7.5.1. Skeletal vibrations

The carbon–carbon stretching modes of the phenyl group are expected

in the range from 1650 to 1200 cm–1

. The actual position of these mode are

determined not so much by the nature of the substituents but by the form of

substitution around the ring [64], although heavy halogens cause undoubtedly

diminish the frequency [65].

Figure 7.6. FT–Raman spectrum of 4–amino–2–methylquinoline (a) Observed

(b) Theoretical HF/6–31G** and (c) HF/6–311++G**

246

In AMQ under CS symmetry the carbon–carbon stretching bands are appeared

in the infrared spectrum at 1617, 1570, 1518, 1470, 1415, 1241 and 1129 cm–1

are

assigned to skeletal CC bonds while the bands at 1593 and 1371 cm–1

have been

assigned to the ring CN stretching vibrations. The corresponding CC and CN

stretching modes are observed in the Raman spectrum are given in Tables 7.4 and 7.5.

The bands occurring at 979 and 759 cm–1

in the infrared and at 983, 752 and

509 cm–1

in Raman spectrum are assigned to the skeletal CCC/CCN in–plane bending

modes of AMQ. The other in–plane bending vibrations of the ring modes are

calculated through ab initio and DFT methods. The out of plane bending ring

vibrations under CS symmetry are assigned to the bands at 648, 619, 538, 449 and 105

cm–1

. The results are in good agreement with the literature values [66–69]. Normal

coordinate analysis shows that significant mixing of skeletal in–plane bending with

C–H in–plane bending and vice versa occurs. In benzene the ring breathing (A1g)

vibrations exhibit the characteristic frequencies at 995 cm–1

[64]. In AMQ the ring

breathing mode is observed at 864 and 872 cm–1

in the infrared and Raman spectra.

The normal co–ordinate analysis predicts that these are very pure modes since their

PED contribution are almost 100%.

7.5.2. Aromatic C–H vibrations

The aromatic compounds show the presence of the C–H stretching vibrations

around 3100–3000 cm–1

range. In AMQ these modes are observed at 3103, 3060 and

3037 cm–1

. The other two wavenumbers are predicted from ab initio calculations.

The C–H in–plane bending vibrations are observed in the region 1350–950 cm–1

and

are usually weak. The C–H out of plane bending modes usually medium intensity

arises in the region 600–950 cm–1

[69–71]. All these C–H in–plane and out of plane

bending modes of the compound are also assigned within the said region and are

presented in the Tables 7.3 and 7.4.

7.5.3. Group vibrations

The frequencies observed at 3399 and 3334 cm–1

in the infrared spectrum are

assigned to the –NH2 asymmetric and symmetric stretching modes of AMQ,

respectively. The theoretical scaled N–H stretching frequencies become slightly

higher than the experimental values at all levels of calculations. Among the other

vibrations of amino group, the strong band in IR at 1659 cm–1

is assigned to the

247

deformation mode. The other fundamental bands of amino group are observed in the

expected region [71–73] and are presented in Tables. Considerable overlapping

between twisting and wagging modes occurs and is confirmed from PED.

The asymmetric stretching and asymmetric deformation modes of the −CH3

group would be expected to be depolarised for A" symmetry species. The νs(CH3)

frequencies are established at 2873 cm−1

in the infrared and νa(CH3) is assigned at

2917 under A' and A" species of AMQ, respectively. The symmetrical methyl

deformational mode is obtained at 1438 cm–1

in IR. The methyl deformational modes

mainly coupled with the C−C in–plane bending vibrations. The −CH3 rocking and

wagging modes of AMQ are given in the Tables. These assignments are substantiated

by the reported literature [36,71–74]. The vibrational assignments of the fundamental

modes are also supported by GaussView molecular visualisation program [75].

A better agreement between the computed and experimental frequencies can

be obtained by using different scale factors for different regions of vibrations.

Initially, all scaling factors have been kept fixed at a value of 1.0 to produce the pure

ab initio calculated vibrational frequencies and the potential energy distributions

(PED) which are given in Tables 7.3 and 7.4. The correction factors used to correlate

the experimentally observed and theoretically computed frequencies for each

vibrational modes of AMQ under HF and DFT–B3LYP methods are similar and an

explanation of this approach were discussed previously [76–83]. Subsequently, in HF

method a scale factor of 0.91 for N−H, ring C−H and methyl C−H stretching modes

while 0.93 for the all other vibrations are used. In B3LYP level a scale factor of 0.96

for N−H, ring C−H and methyl C−H stretching vibrations and 0.99 for other

fundamental modes have been utilised to obtain the scaled frequencies of the

compound AMQ with 6–31G** and 6–311++G** basis sets. The resultant scaled

frequencies are also listed in Tables 7.4 and 7.5. The scale factors used in this study

minimised the deviations very much between the computed and experimental

frequencies both at HF and DFT–B3LYP level of calculations. DFT–B3LYP

correction factors are all much closer to unity than the HF correction factor, which

means that the DFT–B3LYP frequencies are very much closer to the experimental

values than the HF frequencies. Thus, vibrational frequencies calculated by using the

B3LYP functional with 6–31G** and 6–311++G** basis sets can be utilised to

248

eliminate the uncertainties in the fundamental assignments in infrared and Raman

vibrational spectra [84].

7.6. Conclusions

The molecular structural parameters, thermodynamic properties and

vibrational frequencies of the fundamental modes of the optimised geometry of

4–amino–2–methylquinoline have been obtained from quantum mechanical ab initio

and DFT calculations. The geometry was optimised without any symmetry

constraints using the DFT–B3LYP and HF methods with 6–31G** and 6–311++G**

basis sets. The theoretical results were compared with the experimental vibrational

wavenumbers. Although both types of calculations are useful to explain the

vibrational spectral data of AMQ, the deviation between the experimental and

calculated (both unscaled and scaled) frequencies was reduced with the use of DFT–

B3LYP method using high level basis set 6–311++G** in comparison with the HF in

the whole range of calculations and considered as more reliable than the HF method

for large molecule.

249

Table 7.1. Structural parameters calculated for 4–amino–2–methylquinoline employing

HF and B3LYP methods with 6–31G** and 6–311++G** basis set

Structural Parameters

4–amino–2–methylquinoline

HF B3LYP

6–31G** 6–311++G** 6–31G** 6–311++G**

Internuclear Distance (Å)

N1–C2 1.30 1.29 1.32 1.32

C2–C3 1.42 1.42 1.42 1.42

C3–C4 1.36 1.36 1.38 1.38

C4–C9 1.43 1.43 1.44 1.43

C5–C9 1.42 1.42 1.42 1.42

C5–C6 1.36 1.36 1.38 1.38

C6–C7 1.41 1.41 1.41 1.41

C7–C8 1.36 1.36 1.38 1.38

C8–C10 1.42 1.42 1.42 1.42

C9–C10 1.40 1.40 1.43 1.43

N1–C10 1.36 1.38 1.37 1.36

C2–C11 1.51 1.51 1.51 1.51

C4–N12 1.38 1.38 1.39 1.38

C–H (ring)a 1.08 1.08 1.09 1.08

N–H (amino)a 1.00 1.00 1.01 1.01

250

C–H (methyl)a 1.09 1.08 1.10 1.09

Bond Angle (degree)

C2–N1–C10 118.11 118.19 117.59 117.87

N1–C2–C3 123.28 123.18 123.33 123.11

N1–C2–C11 117.70 117.90 117.15 117.44

C3–C2–C11 119.01 118.92 119.52 119.45

C2–C3–C4 120.06 120.10 120.45 120.54

C2–C3–H13 119.46 119.42 119.53 119.44

C4–C3–H13 120.48 120.48 120.01 120.02

C3–C4–N12 121.77 121.60 121.62 121.40

C3–C4–C9 1117.87 117.87 117.80 117.82

C9–C4–N12 120.33 120.49 120.53 120.74

C6–C5–C9 120.78 120.82 120.82 120.88

C6–C5–H14 119.20 119.02 119.10 118.83

C9–C5–H14 120.01 120.15 120.05 120.28

C5–C6–C7 119.95 119.90 120.11 120.07

C5–C6–H15 120.22 120.21 119.97 120.02

C7–C6–H15 119.83 119.89 119.92 119.91

C6–C7–C8 120.42 120.42 120.28 120.31

C6–C7–H16 119.51 119.53 119.66 119.65

C8–C7–H16 120.07 120.05 120.05 120.03

251

a–mean value

C7–C8–C10 120.79 120.80 121.04 121.03

C7–C8–H17 121.76 121.63 121.81 121.67

C10–C8–H17 117.45 117.57 117.15 117.30

C5–C9–C4 123.66 123.67 123.75 123.80

C10–C9–C4 117.10 117.08 117.08 117.08

C10–C9–C5 119.25 119.25 119.17 119.12

C8–C10–C9 118.79 118.79 118.56 118.58

C8–C10–N1 117.65 117.64 117.73 117.85

C9–C10–N1 123.55 123.57 123.71 123.57

C2–C11–H (methyl)a

110.40 110.31 110.63 110.56

H–C11–H (methyl)a

108.53 108.62 108.29 108.36

C4–N12–H (amino)a

115.56 115.71 115.81 116.89

H–N12–H (amino)a

112.14 112.17 112.44 113.27

252

Table 7.2. The calculated thermodynamic parameters of 4–amino–2–methylquinoline employing HF and B3LYP methods with

6–31G** and 6–311++G** basis set

Thermodynamic parameters (298 K)

4–amino–2–methylquinoline

HF/

6–31G**

HF/

6–311++G**

B3LYP/

6–31G**

B3LYP/

6–311++G**

Experimental

values

Quinolinea

SCF Energy (a.u) – 493.44 –493.54 –486.63 –496.74

Total Energy (thermal), Etotal (kcal.mol–1

) 126.68 125.86 119.19 118.51

Heat Capacity at const. volume, Cv (cal.mol–1

.K–1

) 36.85 37.12 39.86 40.18

Entropy, S (cal.mol–1

.K–1

) 94.27 94.94 97.25 100.41

Vibrational Energy, Evib (kcal.mol–1

) 124.90 124.08 117.42 116.73

Zero–point vibrational Energy, E0 (kcal.mol–1

) 120.87 119.98 112.95 112.15

Rotational Constants (GHz)

A 1.60 1.61 1.58 1.59 3.146

B 0.86 0.86 0.85 0.85 1.272

C 0.56 0.56 0.56 0.56 0.906

Dipolemoment (Debye)

µx 0.02 0.13 0.02 0.03 0.144

µy 3.09 3.09 3.27 3.36 2.015

µz –1.03 –0.92 –0.94 –0.77 0.000

µtotal 3.26 3.22 3.41 3.45 2.020

a– values taken from Ref. [63]

253

Table 7.3. Symmetry co–ordinates of 4–amino–2–methylquinolinea.

Symmetry Co–ordinates Description

S1 = r1,2 ν N1C2

S2 = r2,3 ν C2C3

S3 = r3,4 ν C3C4

S4 = r4,9 ν C4C9

S5 = r5,9 ν C5C9

S6 = r5,6 ν C5C6

S7 = r6,7 ν C6C7

S8 = r7,8 ν C7C8

S9 = r8,10 ν C8C10

S10 = r9,10 ν C9C10

S11 = r10,1 ν C10N1

S12 = r2,11 ν C2C11

S13 = r3,13 ν C3H13

S14 = r4,12 ν C4N12

S15 = r5,14 ν C5H14

S16 = r6,15 ν C6H15

S17 = r7,16 ν C7H16

S18 = r8,17 ν C8H17

S19 = r12,21 − r12,22 νa NH2

S20 = r12,21 + r12,22 νs NH2

S21 = 2r11,20 − r11,18 − r11,19 νa CH3

S22 = r11,18 − r11,19 νa CH3

S23 = r11,18 + r11,19 + r11,20 νs CH3

S24 = β1,2,3 + β2,3,4 − 2β3,4,9 + β4,9,10 + β1,10,9 − 2β10,1,2 β ring1

S25 = β1,2,3 − β2,3,4 + β3,4,9 − β4,9,10 + β1,10,9 − β10,1,2 β ring2

S26 = β1,2,3 − β2,3,4 + β4,9,10 − β1,10,9 β ring3

S27 = β9,10,8 − 2β10,8,7 + β8,7,6 − β7,6,5 − 2β6,5,9 + β5,9,10 β ring4

S28 = β9,10,8 − β10,8,7 + β8,7,6 − β7,6,5 + β6,5,9 − β5,9,10 β ring5

S29 = β9,10,8 − β8,7,6 + β7,6,5 + β5,9,10 β ring6

S30 = 2β21,12,22 – β21,12,4 – β22,12,4 δ NH2

S31 = β21,12,4 – β22,12,4 ρ NH2

S32 = β1,2,11 − β3,2,1 β C2C11

254

S33 = β2,3,13 − β4,3,13 β C3H13

S34 = β3,4,12 − β9,4,12 β C4N12

S35 = β9,5,14 – β6,5,14 β C5H14

S36 = β5,6,15 − β7,6,15 β C6H15

S37 = β6,7,16 − β8,7,16 β C7H16

S38 = β7,8,17 − β10,8,17 β C8H17

S39 = 2β20,11,18 – β18,11,19 – β19,11,20 δa CH3

S40 = β18,11,19 – β19,11,20 δa CH3

S41 = β20,11,18 + β18,11,19 + β19,11,20 – β2,11,18 – β2,11,19 – β2,11,20 δs CH3

S42 = 2β2,11,20 – β2,11,19 – β2,11,18 ρ CH3

S43 = γ1,2,3,4 + γ2,3,4,9 − 2γ3,4,9,10 + γ4,9,10,1 + γ9,10,1,2 − 2γ10,1,2,3 γ ring1

S44 = γ1,2,3,4 − γ2,3,4,9 + γ3,4,9,10 − γ4,9,10,1 + γ9,10,1,2 − γ10,1,2,3 γ ring2

S45 = γ1,2,3,4 − γ2,3,4,9 + γ4,9,10,1 − γ9,10,1,2 γ ring3

S46 = γ7,8,10,9 + γ6,7,8,10 − 2γ5,6,7,8 + γ7,6,5,9 + γ6,5,9,10 − 2γ5,9,10,8 γ ring4

S47 = γ7,8,10,9 − γ6,7,8,10 + γ5,6,7,8 − γ7,6,5,9 + γ6,5,9,10 − γ5,9,10,8 γ ring5

S48 = γ7,8,10,9 − γ6,7,8,10 + γ7,6,5,9 − γ6,5,9,10 γ ring6

S49 = γ4,12,21,22 ω NH2

S50 = γ4,12,21 + γ4,12,22 τ NH2

S51 = γ11,2,1,3 γ C2C11

S52 = γ13,3,2,4 γ C3H13

S53 = γ12,4,3,9 γ C4N12

S54 = γ14,5,9,6 γ C5H14

S55 = γ15,6,5,7 γ C6H15

S56 = γ16,7,6,8 γ C7H16

S57 = γ17,8,7,10 γ C8H17

S58 = γ2,11,20 – γ2,11,19 ω CH3

S59 = γ1,10,9,5 − γ8,10,9,4 Butterfly

S60 = τ2,11 CH3 torsion

aν–stretching; β–in–plane bending; δ–deformation; ρ–rocking; γ–out of plane bending;

ω–wagging and τ–twisting/torsion. aDefinitions are made in terms of the standard valance

coordinates; ri,j is the bond distance between the atoms i and j; βi,j,k is the valance angle

between the atoms i,j and k, with j the central atom; γi,j,k is the out of plane angle between

the atoms i,j and k, with j the central atom; γi,j,k,l is the out of plane angle between the i−j

bond and the plane defined by the j,k and l atoms, τi,j is the torsional vibration between

the atoms i and j.

255

Table 7.4. The observed FTIR, FT–Raman and calculated frequencies using HF/6–31G** and B3LYP/6–31G** methods along with their relative

intensities, probable assignments and potential energy distribution (PED) of 4–amino–2–methylquinolinea.

Spec

ies

Observed

wavenumber (cm–1

) HF/6–31G** Calculated wavenumber

B3LYP/6–31G** Calculated

wavenumber

Depola

–

risation

ratio

Assignment %PED

FTIR FTR Unscaled

(cm–1

)

Scaled

(cm–1

)

IR

intensity

Raman

Activity

Unscaled

(cm–1

)

Scaled

(cm–1

)

IR

intensity

A′ 3399 s 3930 3576 21.72 52.29 3690 3542 14.58 0.75 νaNH2 93νNH

A′ 3334 m 3821 3477 27.49 125.87 3583 3440 18.54 0.15 νsNH2 95νNH

A′ 3103 s 3384 3079 13.00 171.65 3215 3086 13.16 0.15 νCH 94νCH

A′ 3372 3069 32.85 128.77 3203 3075 26.84 0.19 νCH 92νCH

A′ 3060 m 3062 m 3356 3054 19.02 102.49 3187 3060 15.97 0.64 νCH 93νCH

A′ 3037 w 3343 3042 7.16 125.93 3177 3050 3.11 0.43 νCH 91νCH

A′ 3342 3041 12.84 38.09 3172 3045 18.68 0.45 νCH 90νCH

A′ 3305 3008 12.44 64.44 3159 3033 7.49 0.70 νaCH3 92νCH

A″ 2917 m 2920 m 3238 2947 28.92 104.65 3095 2971 19.55 0.75 νaCH3 94νCH

A′ 2873 m 3185 2898 30.74 187.40 3041 2919 25.62 0.05 νsCH3 90νCH

2783 m 2 x 1371

2382 vw 2 x 1194

1962 vw 1194 + 845

256

1815 vw 2 x 1371

A′ 1659 s 1837 1708 206.62 16.18 1678 1661 195.50 0.75 δNH2 92δNH2

A′ 1649 vw 1824 1696 136.51 11.41 1672 1655 36.52 0.51 νC=C 83νC=C

A′ 1617 s 1619 vw 1806 1680 102.54 6.91 1646 1630 71.68 0.17 νC=C 89νC=C

A′ 1593 vs 1593 m 1774 1650 71.02 52.86 1613 1597 53.82 0.67 νC=N 82νC=N

A′ 1570 s 1565 m 1679 1561 88.17 1.44 1562 1546 65.37 0.29 νC=C 87νC=C

A′ 1518 s 1517 vw 1638 1523 7.52 13.74 1514 1499 6.26 0.35 νC=C 88νC=C

A″ 1613 1500 5.88 19.61 1498 1483 6.08 0.75 δaCH3 80δCH3 +14βCC

A′ 1607 1495 0.91 41.77 1490 1475 0.86 0.56 δaCH3 77δCH3 + 15βCC

A′ 1470 vw 1464 w 1587 1476 55.25 5.57 1472 1457 43.91 0.29 νC−C 85νCC

A′ 1438 s 1554 1445 16.83 19.80 1430 1416 34.47 0.28 δsCH3 81δCH3 + 12βCC

A′ 1415 w 1408 vw 1515 1409 44.41 44.29 1410 1396 23.13 0.16 νC−C 82νCC

A′ 1491 1387 4.45 24.88 1401 1387 1.47 0.23 νC−C 84νCC

A′ 1371 s 1366 vs 1476 1373 0.69 168.47 1385 1371 2.43 0.17 νC−N 84νCN

A′ 1344 m 1394 1296 4.92 2.64 1308 1295 4.21 0.3 βC−H 74βCH + 16βCCC

A′ 1241 m 1243 vw 1333 1240 15.36 3.73 1274 1261 4.77 0.29 νC−C 85νCC

A′ 1311 1219 11.84 4.39 1215 1203 14.02 0.75 νC−C(H3) 78νCC + 15βCH

A′ 1194 m 1199 vw 1284 1194 2.60 8.35 1197 1185 1.31 0.25 νC−N(H2) 77νCN + 18βCH

A′ 1239 1152 5.02 8.26 1159 1147 0.32 0.53 βC−H 66βCH + 21βCCC

257

A′ 1129 w 1137 w 1191 1108 4.45 2.21 1142 1131 5.80 0.73 νC−C 82νCC

A′ 1174 1092 1.87 0.52 1094 1083 2.67 0.75 βC−H 76βCH + 12βCCC

A′ 1067 vw 1076 vw 1158 1077 3.03 1.29 1058 1047 2.81 0.75 ρCH3 70ρCH3 + 14βCCN

A′ 1032 vw 1032 w 1123 1044 0.55 0.56 1054 1043 3.18 0.74 ρNH2 75ρNH2 + 12βCCC

A′ 1111 1033 4.75 12.53 1017 1007 13.14 0.14 βC−H 72βCH + 18βCCC

A″ 1000 vw 1099 1022 14.66 1.63 997 987 0.33 0.23 ωCH3 65ωCH3 +21γCH

A′ 979 w 983 vw 1085 1009 1.43 0.90 992 982 4.31 0.31 βCCC 74βCCC + 15βCH

A′ 949 vw 959 vw 1052 978 5.76 0.56 952 942 1.09 0.66 βC−H 74βCH + 21βCN

A″ 976 908 7.90 1.74 883 874 4.94 0.62 γC−H 67γCH + 18γCCC

A′ 864 w 872 vw 952 885 6.86 2.43 879 870 2.92 0.25 CCC ring

breathing 92βCCC

A″ 845 s 845 vw 938 872 51.83 3.25 850 842 25.27 0.73 γC−H 69γCH + 15γCCC

A″ 783 m 871 810 0.67 2.24 795 787 1.22 0.71 γC−H 68γCH + 16γCCC

A″ 858 798 58.44 1.44 776 768 40.67 0.59 γC−H 65γCH + 20γCCC

A′ 759 vs 752 w 811 754 1.84 8.81 760 752 0.98 0.12 βCCC 70βCCC + 16βCH

A″ 732 681 51.47 2.62 667 660 18.36 0.66 γC−H 71γCH + 12γCN

A″ 648 w 649 vw 714 664 16.60 3.99 660 653 0.91 0.36 γCCC 69γCCC + 20γCH

A″ 619 w 699 650 28.41 5.02 639 633 37.95 0.16 γCCC 66γCCC + 18γCH

A″ 563 m 564 w 620 577 223.79 6.82 564 558 87.11 0.73 ωNH2 67ωNH2 + 24τNH2

258

A′ 594 552 25.59 4.04 547 542 167.12 0.26 βCNC 68βCNC + 20βCC

A″ 538 vw 539 vw 582 541 2.69 0.25 541 536 21.70 0.33 γCCC 65γCCC + 22γCH

A′ 577 537 9.64 8.65 533 528 0.38 0.15 βCCC 69βCCC + 18βCH

A′ 509 w 546 508 1.74 6.20 509 504 3.51 0.47 βCCN 65βCCN + 22βCC

A″ 449 w 450 w 486 452 6.37 5.69 453 448 2.68 0.42 γCCC 68γCCC + 16γCH

A″ 479 445 14.80 4.11 442 438 19.48 0.61 γCCC 67γCCC + 22γCH

A″ 363 338 31.16 2.44 361 357 28.91 0.68 τNH2 65τNH2 + 25ωNH2

A′ 320 vw 336 312 5.59 0.56 309 306 2.65 0.61 βC−N(H2) 71βCN + 18βCCC

A″ 313 291 10.86 1.10 301 298 1.58 0.75 γC−N(H2) 69γCN + 14γCCC

A′ 280 vw 284 264 2.40 0.71 268 265 0.78 0.61 βC−C(H3) 73βCC + 15βCCN

A″ 215 vw 210 195 1.74 1.30 192 190 1.06 0.75 γC−C(H3) 65γCC + 20γCCN

A″ 173 161 6.39 1.30 160 158 5.61 0.75 γCNC 69γCNC + 16γCH

A″ 105 m 123 114 0.37 2.28 109 108 0.23 0.75 γCCN 67γCCN + 20γCC

A″ 91 s 81 81 0.45 0.02 59 59 0.46 0.74 τCH3

(torsion)

aν–stretching; β–in–plane bending; δ–deformation; ρ–rocking; γ–out of plane bending; ω–wagging and τ–twisting/torsion, wavenumbers, (cm

–1); IR

intensities, ( km/mole); Raman scattering activities, (Å)4/(a.m.u).

259

Table 7.5. The observed FTIR, FT–Raman and calculated frequencies using HF/6–311++G** and B3LYP/6–311++G** force field along with their relative

intensities, probable assignments and potential energy distribution (PED) of 4–amino–2–methylquinolinea.

Sp

ecie

s

Observed

wavenumber (cm–1

) HF/6–311++G** Calculated wavenumber

B3LYP/6–311++G**

Calculated wavenumber Depolari

zation

ratio

Assignment %PED

FTIR FTR Unscaled

(cm–1

)

Scaled

(cm–1

)

IR

intensity

Raman

Activity

Unscaled

(cm–1

)

Scaled

(cm–1

)

IR

intensity

A′ 3399 s 3906 3554 24.20 41.05 3685 3538 21.06 0.75 νaNH2 94νNH

A′ 3334 m 3806 3463 30.89 134.94 3585 3442 26.01 0.13 νsNH2 92νNH

A′ 3103 s 3361 3059 10.19 179.96 3196 3068 10.82 0.15 νCH 95νCH

A′ 3060 m 3062 m 3352 3050 24.45 97.52 3186 3059 20.46 0.24 νCH 90νCH

A′ 3335 3035 14.20 96.70 3170 3043 13.37 0.62 νCH 93νCH

A′ 3037 w 3322 3023 0.45 85.38 3161 3035 2.22 0.59 νCH 92νCH

A′ 3321 3022 17.68 73.32 3155 3029 17.20 0.27 νCH 94νCH

A′ 3280 2985 13.19 61.26 3133 3008 8.16 0.66 νaCH3 92νCH

A″ 2917 m 2920 m 3216 2927 25.17 89.94 3072 2949 17.03 0.75 νaCH3 91νCH

A′ 2873 m 3167 2882 29.73 234.01 3024 2903 25.91 0.05 νsCH3 93νCH

2783 m 2 x 1371

2382 vw 2 x 1194

260

1962 vw 1194 + 845

1815 vw 2 x 1371

A′ 1659 s 1822 1694 248.47 19.85 1667 1650

202.15 0.60 δNH2 93δNH2

A′ 1649 vw 1811 1684 123.52 6.88 1655 1638

30.23 0.38 νC=C 87νC=C

A′ 1617 s 1619 vw 1790 1665 90.06 4.07 1632 1616

99.35 0.43 νC=C 89νC=C

A′ 1593 vs 1593 m 1758 1635 87.54 67.05 1597 1581

64.35 0.61 νC=N 85νC=N

A′ 1570 s 1565 m 1663 1547 96.92 0.95 1546 1531

79.65 0.45 νC=C 87νC=C

A′ 1518 s 1517 vw 1623 1509 8.31 18.29 1500 1485

6.86 0.29 νC=C 86νC=C

A″ 1603 1491 7.62 9.08 1485 1470

8.23 0.75 δaCH3 80δCH3 + 16βCC

A′ 1596 1484 3.41 32.93 1478 1463

2.88 0.43 δaCH3 82δCH3 + 14βCC

A′ 1470 vw 1464 w 1574 1464 61.96 10.42 1460 1445

57.13 0.19 νC−C 88νCC

A′ 1438 s 1540 1432 16.22 14.08 1416 1402

37.66 0.9 δsCH3 85δCH3 + 12βCC

A′ 1415 w 1408 vw 1499 1394 50.49 62.16 1395 1381

32.32 0.12 νC−C 89νCC

A′ 1478 1375 6.17 20.89 1386 1372

2.95 0.29 νC−C 85νCC

A′ 1371 s 1366 vs 1460 1358 2.00 224.53 1372 1358

2.54 0.14 νC−N 82νCN

A′ 1344 m 1387 1290 5.21 2.42 1300 1287

4.07 0.75 βC−H 75βCH + 15βCCC

261

A′ 1241 m 1243 vw 1322 1229 17.03 5.62 1265 1252

8.62 0.23 νC−C 84νCC

A′ 1302 1211 12.60 3.21 1210 1198

15.97 0.67 νC−C(H3) 76νCC + 16βCH

A′ 1194 m 1199 vw 1275 1186 2.81 12.02 1192 1180

1.52 0.12 νC−N(H2) 79νCN + 12βCH

A′ 1170 vw 1231 1145 6.80 8.43 1152 1140

0.66 0.35 βC−H 68βCH + 20βCCC

A′ 1129 w 1137 w 1181 1098 4.84 2.30 1136 1125

9.23 0.62 νC−C 87νCC

A′ 1165 1083 3.23 0.68 1085 1074

4.25 0.72 βC−H 76βCH + 14βCCC

A′ 1067 vw 1076 vw 1153 1072 1.79 0.23 1054 1043

1.75 0.71 ρCH3 75ρCH3 + 14βCCN

A′ 1032 vw 1032 w 1109 1031 0.27 1.12 1047 1037

4.97 0.64 ρNH2 73ρNH2 + 15βCCC

A′ 1101 1024 5.74 20.97 1011 1001 15.85 0.09 βC−H 72βCH + 18βCCC

A″ 1000 vw 1091 1015 17.35 0.67 995 985

0.36 0.46 ωCH3 69ωCH3 +18γCH

A′ 979 w 983 vw 1080 1004 1.10 2.54 987 977

4.09 0.50 βCCC 74βCCC + 12βCH

A′ 949 vw 959 vw 1043 970 5.06 0.76 958 948

1.10 0.75 βC−H 74βCH + 18βCN

A″ 966 898 7.32 0.88 883 874

4.78 0.45 γC−H 66γCH + 21γCCC

A′ 864 w 872 vw 947 881 5.72 3.29 872 863 4.53 0.20 CCC ring

breathing 90βCCC

A″ 845 s 845 vw 932 867 44.65 1.67 846 838 23.29 0.75 γC−H 69γCH + 15γCCC

A″ 783 m 869 808 2.79 0.29 793 785 5.04 0.56 γC−H 67γCH + 16γCCC

A″ 849 790 73.99 1.14 768 760 63.11 0.62 γC−H 67γCH + 20γCCC

A′ 759 vs 752 w 806 750 1.69 11.58 758 750 0.87 0.05 βCCC 67βCCC + 19βCH

262

A″ 726 675 39.38 2.74 662 655 4.95 0.30 γC−H 72γCH + 14γCN

A″ 648 w 649 vw 709 659 9.94 4.51 659

652 1.23 0.16 γCCC 69γCCC + 14γCH

A″ 619 w 697 648 22.22 4.62 632

627 18.13 0.10 γCCC 68γCCC + 16γCH

A″ 563 m 564 w 614 571 186.02 6.38 560

554 7.57 0.41 ωNH2 65ωNH2 + 24τNH2

A′ 590 549 35.75 2.90 540

535 2.38 0.30 βCNC 66βCNC + 22βCC

A″ 538 vw 539 vw 578 538 2.66 0.59 531

526 2.53 0.41 γCCC 68γCCC + 18γCH

A′ 573 533 11.08 9.78 510 505

45.60 0.11 βCCC 70βCCC + 18βCH

A′ 509 w 544 506 1.79 6.45 505

500 186.27 0.38 βCCN 67βCCN + 18CC

A″ 449 w 450 w 483 449 5.99 7.17 452

447 2.44 0.29 γCCC 65γCCC + 18γCH

A″ 477 444 16.92 2.68

438 434

31.54 0.61 γCCC 67γCCC + 22γCH

A″ 356 331 24.16 0.74

351 347

26.53 0.73 τNH2 66τNH2 + 24ωNH2

A′ 320 vw 332 309 4.88 0.43

305 302

2.40 0.48 βC−N(H2) 72βCN + 15βCCC

A″ 312 290 10.46 0.93

303 300

1.38 0.69 γC−N(H2) 70γCN + 16γCCC

A′ 280 vw 285 265 2.25 0.71

270 267

1.05 0.54 βC−C(H3) 75βCC + 15βCCN

A″ 215 vw 208 193 1.62 0.91

188 186

0.96 0.75 γC−C(H3) 69γCC + 14γCCN

A″ 171 159 7.88 0.80

157 155

7.50 0.75 γCNC 67γCNC + 18γCC

263

A″ 105 m 120 112 0.53 1.05

104 103

0.35 0.75 γCCN 65γCCN + 20γCC

A″ 91 s 65 65 0.33 0.15

15 15 0.23 0.75 τCH3

(torsion)

aν–stretching; β–in–plane bending; δ–deformation; ρ–rocking; γ–out of plane bending; ω–wagging and τ–twisting/torsion, wavenumbers, (cm

–1); IR

intensities, ( km/mole); Raman scattering activities, (Å)4/(a.m.u); Reduced mass, (a.m.u); and Force constant, (mdyne/Å).

264

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