Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 277–284

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Thermal and magnetic properties and vibrational analysis of 4-(dimethylamino) pyridine: A quantum chemical approach V. Balachandran a,⇑, S. Rajeswari b, S. Lalitha b Centre for Research, Department of Physics, A A. Government Arts College, Musiri 621 211, India P.G. & Research Department of Physics, Periyar EVR College(Autonomous), Tiruchirappalli 620 023, India

g r a p h i c a l a b s t r a c t

 The FT-IR and FT-Raman spectra of

0.0000008

a r t i c l e

i n f o

Article history: Received 16 November 2013 Received in revised form 9 December 2013 Accepted 10 January 2014 Available online 18 January 2014 Keywords: 4DMAP HOMO–LUMO Vibrational spectra NBO FT-IR FT-Raman

Magnetic susceptibility

4-(dimethylamino) pyridine were recorded and analyzed.  The complete vibrational assignments and spectroscopic analysis were made.  The HOMO, LUMO energy gap were theoretically predicted.  Temperature dependence thermodynamic parameters and magnetic properties have been analyzed.  The magnetic susceptibility for various temperatures are predicted.

0.0000007 0.0000006 0.0000005 0.0000004 0.0000003 0.0000002 0.0000001

4 00 6 0. 00 8 0. 01 0 0. 01 2 0. 01 4 0. 01 6 0. 01 8 0. 02 0 0. 02 2 0.

2

00

0.

00

0

0.0000000

0.

h i g h l i g h t s

00

b

0.

a

Temperature−1 (Kelvin)

a b s t r a c t The FT-IR and FT-Raman spectra of 4-(dimethylamino) pyridine (4DMAP) have been recorded in the region 4000–500 cm1and 3500–100 cm1. Quantum chemical calculations of energy, geometry and vibrational wavenumbers of 4DMAP were carried out by using ab initio HF and density functional theory (DFT/B3LYP) with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. The harmonic vibrational wavenumbers were calculated and the scaled wavenumbers have been compared with the experimental FT-IR and FT-Raman spectra. The quantum chemical parameters have been computed from the HOMO–LUMO energy values. Temperature dependence thermodynamic parameters and magnetic properties of the title compound have been analyzed. Using NBO analysis the stability of the molecule arising from hyper-conjugative interactions, charge delocalization has been analyzed. The first-order hyper-polarizability (b) values of the title molecule were computed by B3LYP method. Finally the theoretically spectrograms for FT-IR and FT-Raman spectra of the title molecule have been constructed which show good agreement with recorded spectra. Crown Copyright Ó 2014 Published by Elsevier B.V. All rights reserved.

Introduction Pyridine, also called azobenzene and amine, is a heterocyclic aromatic tertiary arnine characterized by a six-member ring structure composed of five carbon atoms and one carbon–hydrogen unit in the benzene ring being replaced by a nitrogen atom. The simplest member of the pyridine family is pyridine itself. It is colorless, ⇑ Corresponding author. Tel.: +91 431 2591338; fax: +91 4326 262630. E-mail address: [email protected] (V. Balachandran).

flammable, toxic liquid with an unpleasant odor, miscible with water and with most organic solvents, boils at 115 °C. It is made from crude coal tar or from other chemicals based on acetaldehyde and ammonia. Aminopyridines are obtained from pyridine, when an amino group is replaced a hydrogen attached to the ring. Aminopyridines find wide application in pharmacological industry and in analytical chemical laboratories. They serve as good anesthetic agent and hence used in the preparation of drugs for certain brain disease, particularly 4-aminopyridines is an effective medicine in the treatment for multiple sclerosis [1]. The 3,4-diaminopyridine

1386-1425/$ - see front matter Crown Copyright Ó 2014 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2014.01.023

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V. Balachandran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 277–284

plays an effective role in the symptomatic treatment of multiple sclerosis fatigue like 4-aminopyridine [2]. Pyridine derivatives are used as non-linear materials [3]. Many substituted pyridines are involved in bioactivities with applications in pharmaceutical drugs and agricultural products [4–6]. Pyridine derivatives act as anesthetic agents, drugs for certain brain diseases, and prodrugs for treating neuronal damage caused by stroke. The picoline derivatives prepared from aminopyridine derivatives have been shown to have cholesterol lowering properties, anti-cancer and antiinflammatory agents [4]. The various studies on monosubstituted halo and methylpyridines [7], 2-iodopyridine [8], 2,6-dichloropyridine [9], di-, tri-halopyridines [10,11], 5-bromo-2-nitropyridine [12], 2-chloro-5-bromopyridine [13], 2-fluoro-5-bromopyridine [14] and 2-chloro-6-methoxypyridine [15] were reported. FT-IR and FT-Raman spectra and ab initio DFT vibrational analysis of 2-chloro-5-aminopyridine was reported by Sundaraganesan et al. [16]. The FT-Raman and infrared spectra of 2-hydroxy-4-methyl3-nitropyridine and 2-hydroxy-4methyl-5-nitropyrdine were reported by Balachandran et al. [17]. Arjunan et al. [18] discussed a comparative study on vibrational, conformational and electronic structure of 2-(hydroxymethyl) pyridine and 3-(hydroxymethyl) pyridine. Literature survey reveals that to the best of our knowledge, no ab initio HF and DFT method of the vibrational analysis of 4DMAP have been reported so far. Therefore, the present investigation is undertaken to study the vibrational spectra of this molecule completely and to identify the various normal modes with greater wavenumber accuracy. Ab initio HF and density functional theory (DFT) calculations have been performed to support our wavenumber assignments. The redistribution of electron density (ED) in various bonding and antibonding orbital and energies have been calculated by natural bond orbital (NBO) analysis by DFT method to give clear evidence of stabilization originating from the hyperconjugation of various intra-molecular interactions. The HOMO and LUMO analysis have been used to elucidate information regarding charge transfer within the molecule.

levels to characterize all stationary points as minima. Then vibrationally averaged nuclear positions of 4DMAP were used for harmonic vibrational frequency calculations, IR and Raman intensities and Raman depolarization ratios. We have utilized the gradient corrected density functional theory (DFT) [21] with the three-parameter hybrid functional (B3) [22] for the exchange part and the Lee–Yang–Parr (LYP) correlation function [23], accepted as a cost-effective approach, for the computation of molecular structure, vibrational wavenumbers and energies of optimized structures. Vibrational wavenumbers computed at DFT level have been adjusted to be more reliable than those obtained by HF method. Finally, the calculated normal mode vibrational wavenumbers provide thermodynamic properties also through the principle of statistical mechanics. By combining the result of the GAUSSVIEW program [24] with symmetry considerations, vibrational frequency assignments were made with a high degree of accuracy. The natural bonding orbitals (NBO) calculation [25] were performed using NBO 3.1 program as implemented in Gaussian 09W [19] package at B3LYP/631++G(d,p) level in order to understand various second-order interactions between the filled orbitals of one subsystem and vacant of another subsystem, which is a measure of the intermolecular delocalization or hyper-conjugation. Prediction of Raman intensities The Raman activities (Si) calculated by the Gaussian 09W program were converted to relative Raman intensities (Ii) using the following relationship derived from the basic theory of Raman scattering [26–28].

Ii ¼

f ðt0  ti Þ4 Si ti ½1  expðhcti =kTÞ

ð1Þ

where t0 is the exciting frequency in cm1, ti the vibrational wave number of the ith normal mode, h, c and k are the universal constants and f is the suitably chosen common scaling factor for all the peak intensities.

Experimental details The crystalline sample of 4DMAP is purchased from Sigma Aldrich Chemical Suppliers with the stated purity of 98%. Then the compound is used for spectral measurements without further purification. In the present study, the Fourier transform infrared spectrum (FT-IR) of the title compound is recorded in the wavenumber region 4000–400 cm1 on a NEXUS 670 spectrophotometer equipped with an MCT detector in a KBr pellet technique. The FT-Raman spectrum is recorded in the wavenumber region 3500–100 cm1 on a NEXUS 670 spectrophotometer equipped with Raman module accessory operating at 1.5 W power with Nd:YAG laser of wavelength 1064 nm is used as an excitation source. The spectral measurements were carried out at Sree Chitra Tirunal Institute for Medical Sciences and Technology, Poojappura, Thiruvanathapuram, Kerala, India. Computational details The entire calculation was performed at the HF and DFT level of theory using the 6-311++G(d,p) basis set on personal computer using Gaussian 09W [19] program package, invoking gradient geometry optimization [20]. Initial geometry generated from standard geometrical parameters was minimized without any constraint in the potential energy surface at Hartree–Fock level, adopting the standard 6-311++G(d,p) basis set. The optimized structural parameters were used in the vibrational frequency calculations at the HF/6-311++G(d,p) and DFT/B3LYP/6-311++G(d,p)

Potential energy distribution To check whether the chosen set of symmetric coordinates contribute maximum to the potential energy associated with the molecule, the PED has been carried out. The vibrational problem was set up in terms of internal and symmetry coordinates. The Cartesian representation of the theoretical force constants has been computed at the fully optimized geometry by assuming Cs point group symmetry. The symmetry of the molecule was also helpful in making vibrational arrangement. The transformation of force field, subsequent normal coordinate analysis and calculation of the PED were done on PC with the MOLVIB program (versionV7.0–G77) written by Sundius [29,30]. First-order hyper-polarizability The first hyper-polarizability (b0) of this novel molecular system and related properties (b, a0 and Da) of 4DMAP are calculated using HF/6-311++G(d,p) and DFT/6-311++G(d,p) method based on the finite-field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field. First hyper-polarizability is a third rank tensor that can be described by a 3  3  3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to the Kleinman symmetry [31]. It can be given in the lower tetrahedral format. It is obvious that the lower part of the 3  3  3 matrices is a tetrahedral. The components of b are defined as the coefficients in the Taylor series

V. Balachandran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 277–284

expansion of the energy in the external electric field. When the external electric field is weak and homogeneous, the expansion becomes: 0

E ¼ E  la F  1=2aab FF b  1=6babc FF b F c þ . . .

ð2Þ

where E0 is the energy of the unperturbed molecules, Fa the field at the origin, la, a ab and babc are the components of dipole moment, polarizability and the first hyper-polarizabilities respectively. The total static dipole moment l, the mean polarizability a0, the anisotropy of the polarizability c and the mean first hyper-polarizability btotal using the x, y, z components they are defined as 1

l ¼ ðl2x þ l2y þ l2z Þ2

ð3Þ

a0 ¼ 1=3ðaxx þ ayy þ azz Þ

ð4Þ

c¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðððaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 þ 6ða2xy þ a2yz þ a2zx ÞÞ=2Þ

ð5Þ

btotal

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ ðb2x þ b2y þ b2z Þ

ð6Þ

and

bx ¼ bxxx þ bxyy þ bxzz by ¼ byyy þ byxx þ byzz bz ¼ bzzz þ bzxx þ bzyy Using the HF/6-311++G(d,p) and DFT (6-311++G(d,p) method, energy, dipole moment, mean polarizability, anisotropy of the polarizability and the mean first-order hyper-polarizability of the molecule 4DMAP are calculated and presented in the Table S1(Supporting Material). The calculated first-order hyper-polarizability (btotal) of 4DMAP is 0.5807  1030 esu in HF and 0.5628  1030 esu in B3LYP method. This value is nearly three times that of Urea (0.1947  1030 esu). Results and discussion Molecular geometry Molecular symmetry can be used to predict many molecular properties, such as its dipole moment and its allowed spectroscopic transitions. The labeling of the atoms in 4DMAP is given in Fig. 1 and the global minimum energy obtained by HF and DFT with the standard basis set 6-311++G(d,p) are found to be 379.8717 au. and 382.3601 au, respectively. The optimized geometrical parameters of the title compound calculated by HF/6311++G(d,p) and B3LYP/6-311++G(d,p) are presented in Table 1. Table 1 compares the calculated bond lengths and bond angles for 4DMAP with those experimentally available from X-ray diffraction data [32,33].

Fig. 1. Geometrical structure of 4-(dimethylamino) pyridine.

279

Vibrational assignments The optimized structural parameters were used to compute the vibrational wavenumbers of 4DMAP at HF and DFT/B3LYP/6311++G(d,p) level of calculations. The molecule has 19 atoms and 51 fundamental vibrations of the molecule are distributed as 35 in-plane and 16 out-of-plane vibration. All the vibrations are active in both IR and Raman. The molecule possesses C1 point group symmetry. The harmonic vibrational wavenumbers calculated for 4DMAP at HF and B3LYP levels using the standard basis set has been presented in Table 2. Comparison of the wavenumbers calculated at HF and B3LYP with the experimental values reveals the overestimation of the calculated vibrational modes due to neglect of anharmonicity in real system. Inclusion of electron correlation in density functional theory to a certain extent makes the frequency values smaller in comparison with the HF frequency data. Reduction in the computed harmonic vibrations, though basis set sensitive are marginal as observed in the DFT values using 6-311++G(d,p). Any way notwithstanding the level of calculations, it is customary to scale down the calculated harmonic wavenumbers in order to improve the agreement with the experimental wavenumbers. In our present work, we have used two different scaling factors, i.e. group scaling and scale equation. In group scaling procedure the scale factor 0.9048 below 1000 cm1, 0.9079 is used in the range 1000–1800 cm1 and 0.9103 above 1800 cm1 in HF method and in B3LYP the scale factor 0.991 for the wavenumber less than 1000 cm1, 0.981 for the range 1000–1800 cm1 and 0.9585 above 1800 cm1. Using this procedure the calculated wavenumbers are scaled and are entered in column scaleda in Table 2. In the scaledb column the theoretically calculated wavenumbers are scaled by the equation, which are given at the bottom of Table 2. The IR and Raman intensities have been included in Table 2. Fig. S1 (Supporting Material) represents the comparison plot of calculated frequency with IR and Raman intensities by HF/6-311++G(d,p) and B3LYP/6-311++G(d,p). The RMS deviation between unscaled wavenumbers and the observed wavenumbers for 4DMAP was approximately 158.34 cm1 and 60.24 cm1 at HF and B3LYP method, respectively. For group scaling and scale equation, the RMS deviation between the scaled and observed wavenumbers is found to be 18.00 cm1 and 18.03 cm1 respectively in HF method. In B3LYP method the RMS deviation between the experimental and scaled wavenumbers is found to be 15.46 cm1 and 19.16 cm1, for group scaling and scale equation respectively. The standard deviation difference between the observed, theoretically calculated wavenumbers and scaled wave numbers are predicted and are reported in Table 2. For visual comparison, the observed and stimulated FTIR and FT-Raman spectra of the title compounds are presented in Figs. 2 and 3, which help to understand the observed spectral features. CH vibration The CH stretching vibration of nitrogen heterocyclic aromatic compounds gives rise to a band at 3100–3000 cm1. The bands due to CH in-plane bending vibrations interact somewhat with the CC stretching vibrations; they are observed as a number of bands in the region 1500–1100 cm1. Strong bands observed in the region 850–690 cm1 which are characteristic of the position of the substitution, these bands being due to CH out-of-plane deformation vibrations [34]. In this region the bands are not affected appreciably by the nature of the substituent. Hence, in the present investigation, the FT-IR weak bands identified at 3080 cm1 and 3000 cm1 and the FT-Raman bands identified at 3026 cm1 with a medium intensity and a weak band at 3000 cm1 are assigned to the CH stretching vibrations. The weak band at 1278 cm1, very strong band at 1222 cm1, and the medium bands at

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Table 1 Geometrical parameters of 4-(dimethylamino) pyridine.

a

Geometrical parameters

Theoretical values

Bond length (A°)

HF

B3LYP

N1–C2 N1–C6 C2–C3 C2–H7 C3–C4 C3–H8 C4–C5 C4–N9 C5–C6 C5–H18 C6–H19 N9–C10 N9–C14 C10–H11 C10–H12 C10–H13 C14–H15 C14–H16 C14–H17

1.3208 1.3209 1.3792 1.0774 1.4039 1.0712 1.404 1.3646 1.3791 1.0712 1.0774 1.4476 1.4476 1.0871 1.0802 1.0871 1.0871 1.0871 1.0802

1.338 1.3381 1.3879 1.0871 1.4128 1.0811 1.4129 1.3733 1.3878 1.0811 1.0871 1.4545 1.4545 1.0965 1.0886 1.0965 1.0965 1.0965 1.0886

Expt.a values

1.340 1.340 1.081 1.081 1.394 1.394 1.081 1.081

Geometrical parameters

Theoretical values

Bond angle (°)

HF

B3LYP

C2–N1–C6 N1–C2–C3 N1–C2–H7 C3–C2–H7 C2–C3–C4 C2–C3–H8 C4–C3–H8 C3–C4–C5 C3–C4–N9 C5–C4–N9 C4–C5–C6 C4–C5–H18 C6–C5–H18 N1–C6–C5 N1–C6–H19 C5–C6–H19 C4–N9–C10 C4–N9–C14 C10–N9–C14 N9–C10–H11 N9–C10–H12 N9–C10–H13 H11–C10–H12 H11–C10–H13 H12–C10–H13 N9–C14–H15 N9–C14–H16 N9–C14–H17

115.698 125.0806 116.0568 118.8627 119.2129 118.9045 121.8826 115.7158 122.1444 122.1398 119.2131 121.8789 118.908 125.0796 116.054 118.8664 120.1368 120.1452 119.718 111.7102 109.169 111.7211 107.864 108.3596 107.87 111.7213 111.7103 109.1699

115.5113 124.9354 115.9736 119.0909 119.4165 119.0309 121.5526 115.7869 122.1066 122.1066 119.4206 121.5474 119.0321 124.9294 115.9669 119.1037 120.123 120.1423 119.7348 111.7594 109.1314 111.7672 107.9446 108.1433 107.9512 111.7697 111.7611 109.1244

H15–C14–H16

108.3591

108.1475

H15–C14–H17

107.8697

107.9505

H16–C14–H17

107.8636

107.9437

Expt.a values

117.3

120.2 118.5

118.1 120.8 123.3

Geometrical parameters

Theoretical values

Dihedral angles (°)

HF

B3LYP

C6–N1–C2–C3 C6–N1–C2–H7 C2–N1–C6–C5 C2–N1–C6–H19 N1–C2–C3–C4 N1–C2–C3–H8 H7–C2–C3–C4 H7–C2–C3–H8 C2–C3–C4–C5 C2–C3–C4–N9 H8–C3–C4–C5 H8–C3–C4–N9 C3–C4–C5–C6 C3–C4–C5–H18 N9–C4–C5–C6 N9–C4–C5–H18 C3–C4–N9–C10 C3–C4–N9–C14 C5–C4–N9–C10 C5–C4–N9–C14 C4–C5–C6–N1 C4–C5–C6–H19 H18–C5–C6–N1 H18–C5–C6–H19 C4–N9–C10–H11 C4–N9–C10–H12 C4–N9–C10–H13 C14–N9–C10– H11 C14–N9–C10– H12 C14–N9–C10– H13 C4–N9–C14–H15 C4–N9–C14–H16 C4–N9–C14–H17 C10–N9–C14– H15 C10–N9–C14– H16 C10–N9–C14– H17

0.0012 179.9954 0.0012 179.9953 0.0023 179.9913 179.996 0.0027 0.001 179.999 179.993 0.0076 0.0012 179.992 179.999 0.0077 0.0536 179.947 179.946 0.0528 0.0024 179.996 179.9912 0.0027 60.6845 179.8919 60.8866 119.315

0.0006 179.999 0.0008 179.999 0.0015 179.994 179.9996 0.0078 0.0009 179.9991 179.993 0.0067 0.0003 179.993 179.9997 0.0075 0.0745 179.928 179.926 0.0719 0.0012 179.9995 179.9937 0.0081 60.5995 179.9131 60.7603 119.398

0.1074

0.0844

119.1142

119.2423

60.887 60.6835 179.8911 119.1122

60.7672 60.6009 179.91 119.2302

119.317

119.402

0.1097

0.0926

Values taken from Refs. [30,31].

1102 cm1 and 1068 cm1 in FT-IR are due to the CH in-plane bending vibrations. In FT-Raman, the two weak bands are observed at 1273 cm1 and 1234 cm1 are assigned to the CH in-plane bending vibrations. The CH out-of-plane bending vibration bands are observed at 989 cm1and 807 cm1 as a strong and 943 cm1 as a medium band in FT-IR spectrum. In FT-Raman, the weak band at 994 cm1 is observed for the CH out-of-plane bending vibration. Methyl group (CH3) vibrations The compound under consideration 4DMAP possess a CH3 group in the side substitution chain. There are nine fundamentals one can expect to a CH3 group, namely the symmetrical CH3 stretching, the two asymmetrical CH3 stretching, in-plane bending, out-of-plane bending, in-plane rocking out-of-plane rocking, symmetric bending and torsion [35]. Each methyl group has three stretching vibrations, one being symmetric and other two asymmetric. Methyl groups attached to unsaturated carbons including aromatic groups, absorb in the range 3010–2905 cm1 due to the asymmetric stretching vibration, the symmetric stretching band occurring in the region 2945–2845 cm1. The methyl groups of hydrocarbons give rise to two vibration bands, the asymmetric

deformation band occurring at 1465–1440 cm1 and the symmetric band at 1390–1370 cm1. The intensity of the methyl symmetric vibration band relative to the higher-frequency band may be used to indicate the relative number of methyl groups in the sample. The presence of adjacent atoms or groups can alter the position of the methyl symmetric band significantly, its range being 1470–1260 cm1, whereas the asymmetric band is far less sensitive, its range being 1485–1400 cm1. Methyl rocking vibration band may be of variable intensity occurs in the region 1100–1020 cm1. The CH3 torsional vibration band is in the range 270–130 cm1 [32]. In our study, the weak band at 2977 cm1 in FT-IR is assigned to the CH3 asymmetric stretching vibration. For the symmetric stretching vibration of CH3, the medium bands are observed at 2886 cm1 and 2806 cm1 in FT-IR spectrum. The weak intensity band at 2935 cm1 in FT-Raman is observed and this is due to the CH3 asymmetric stretching vibration. The in-plane CH3 bending vibration is observed at 1517 cm1 in FT-IR with a mediumto-strong intensity. The weak band identified at 1420 cm1 in FTIR is assigned to the out-of-plane CH3 bending vibration. For the symmetric bending vibration of methyl group the band at 1443 cm1 in FT-IR is identified. Methyl rocking vibration band is observed as strong band at 1032 cm1 in FT-Raman spectrum.

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Table 2 The observed FT-IR, FT-Raman and calculated frequencies determined by HF and B3LYP method with 6-311++G(d,p) basis set along with their relative IR and Raman intensities, vibrational assignments and potential energy distribution (PED) of 4-(DMAP). Mode no.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 RMS mean deviation (cm1) Standard deviation (observed) (911.56) Standard deviation difference

Experimental wave number

Theoretical wave number (cm1) Unscaled

Scaleda

FT-IR

HF

B3LYP

HF

B3LYP

HF

B3LYP

HF

B3LYP

HF

B3LYP

3381 3381 3315 3312 3287 3266 3199 3197 3157 3149 1784 1735 1673 1654 1639 1617 1612 1609 1581 1565 1503 1493 1406 1350 1299 1239 1238 1235 1212 1176 1166 1121 1080 1079 1038 911 900 816 811 729 597 588 512 447 410 293 266 201 161 66 42 150 999.9

3209 3208 3143 3140 3135 3122 3036 3035 3000 2992 1637 1580 1546 1526 1514 1493 1486 1485 1459 1447 1393 1375 1322 1255 1253 1198 1140 1136 1125 1087 1079 1005 990 966 959 827 813 761 746 681 549 542 480 403 381 266 243 175 137 79 45 60 954.78

3078 3078 3018 3015 2992 2973 2912 2910 2874 2867 1620 1575 1519 1502 1488 1468 1464 1461 1435 1421 1365 1355 1277 1226 1179 1125 1124 1121 1100 1068 1059 1018 981 980 942 824 814 738 734 660 540 532 463 404 371 265 241 182 146 60 38 18 911.0

3076 3075 3013 3010 3005 2992 2910 2909 2876 2868 1607 1551 1518 1498 1486 1466 1459 1458 1432 1420 1367 1350 1298 1232 1230 1176 1119 1115 1104 1067 1059 987 972 948 941 820 806 754 739 675 544 537 476 399 378 264 241 173 136 78 43 15 910.17

3076 3076 3016 3013 2990 2971 2910 2908 2872 2865 1621 1577 1520 1503 1489 1469 1464 1462 1436 1422 1365 1356 1277 1226 1179 1125 1124 1121 1100 1067 1058 1017 980 979 942 826 816 739 735 660 540 532 462 403 369 263 238 179 143 56 34 18 910.9

3085 3084 3022 3019 3014 3002 2920 2919 2885 2878 1585 1531 1498 1479 1468 1448 1441 1440 1415 1404 1352 1335 1284 1220 1219 1166 1111 1107 1096 1060 1053 982 968 945 938 812 799 749 735 673 547 540 481 408 387 277 255 190 154 99 66 19 910.86

2.64 14.91 16.06 41.70 59.83 3.38 95.60 0.04 22.50 101.70 358.14 100.72 222.75 5.75 3.09 13.03 43.71 0.00 0.01 5.12 193.25 20.48 10.39 49.79 18.60 43.85 0.00 1.44 0.04 0.04 25.17 0.00 71.33 0.12 11.52 0.00 76.26 0.11 7.93 0.23 24.97 1.11 3.36 0.00 0.15 6.05 0.11 0.00 0.00 0.00 2.47

10.52 8.40 10.84 39.79 34.71 2.41 76.62 0.25 37.53 98.12 330.74 47.40 144.15 5.52 5.27 15.25 25.11 0.00 0.65 0.59 122.83 9.38 0.62 44.21 33.62 5.25 0.00 0.02 2.43 0.15 24.97 46.34 0.00 11.50 0.09 0.00 54.81 5.58 0.02 0.31 1.32 19.22 3.09 0.00 0.48 5.32 0.18 0.00 0.00 0.00 1.13

10.30 0.74 8.68 7.83 12.81 0.00 0.40 11.00 24.70 0.68 16.15 1.09 3.55 2.84 0.18 6.74 3.61 2.66 0.15 3.38 13.92 0.45 1.22 3.40 6.64 9.79 1.34 0.38 0.77 5.48 0.02 0.12 21.01 0.21 15.33 0.94 0.46 0.01 20.20 6.41 1.56 4.08 6.22 0.47 14.41 0.08 0.42 1.15 24.45 100.00 11.7

6.78 9.27 14.41 11.44 15.23 0.03 2.44 19.04 39.63 3.88 15.77 0.74 0.92 6.75 0.06 9.10 3.15 4.47 0.39 5.76 4.38 0.16 9.74 0.23 5.66 8.33 1.36 0.52 0.03 6.31 0.52 21.77 0.28 21.69 0.08 0.66 0.58 26.52 0.09 7.27 3.35 1.77 10.56 0.83 28.07 0.13 0.88 2.69 41.57 100.00 13.08

88.34

43.22

0.56

1.39

0.66

0.70

FTRaman

3080w

3000w 2977w

3026m 3000w

2935w 2886m 2806m 1608vs

1604w 1578w

1534m 1517ms 1443ms

1420w 1381s 1278w

1383w 1273w

1222vs

1234w 1162w 1136w

1102m 1068m 989s

1032vs 994w

943m 935w 807s 750ms 721s 670w 534m 523w 482w

539m

397w 362w 273w 234m 208w 129

Infrared intensity

Scaledb

Raman intensity

Vibrational assignments/PED (%)

mCH(100) mCH(99) mCH(97) mCH(99) CH3asym(99) CH3asym(93) CH3asym(91) CH3asym(87) CH3sym(81) CH3sym(79) mCC(85) mCN(79) mCC(73) Ipb CH3(71) Ipb CH3(65) sbCH3(55) opbCH3(48) sbCH3(53) opbCH3(49) mCC(55) mCN(CH3)(44) bCH(69) mCN(CH3)(47) bCH(49) mCC(42) mCN(57) Opr CH3(48) Opr CH3(45) bCH(47) bCH(63) iprCH3(40) cCH(65) mCN(CH3)(54) cCH(43) iprCH3(39) cCH(71) cCH(68) Ring sym(58) Ring asym(59) Ring trigd(46) Tring trigd(63) bCN(CH3)(56) bCN(CH3)(51) Tring sym(49) bCN(CH3)(56) dCH3(64) cCN(CH3)(51) dCH3(56) cCN(CH3)(68) Tring asym(45) iCH3(43)

Abbreviations used: s – torsion; c – out-of-plane bending; b – in-plane bending; t – stretching; ipr – in-plane rocking; opr – out-of-plane rocking; sym – symmetric; asym – asymmetric; sb – symmetric bending; ipb – in-plane bending; opb – out-of-plane bending. a 0.911mcal  4.033 = m exp (HF). b 0.954mcal + 23.18 = m exp (B3LYP).

The torsional vibration of methyl group is identified at 273 cm1 in FT-Raman spectrum with the weak intensity. CC vibration The carbon–carbon stretching modes of the pyridine ring appear in the region 1650–1200 cm1 are determined not so much by the nature of the substituent but by the form of substitution around the ring [36,37]. In 4DMAP, the C–C stretching bands in

the infrared spectrum appeared at 1608 cm1 (s), 1534 cm1 (m). The bands observed at 1604 cm1 (w), 1518 cm1 (w) and 1162 cm1 (w) in FT-Raman spectrum are assigned to the ring carbon–carbon stretching vibrations. All other observed CCC in-plane and out-of-plane bending vibrations of the compounds are completely assigned and are presented in Table 2. The CCC in-plane bending vibrations of 4DMAP are observed in FT-IR spectrum at 750 cm1 (medium-to-strong) and 670 cm1 (weak) and a strong

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V. Balachandran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 277–284 Isodensity plots of FMO’s

Energy (a.u)

Energy gap (a.u)

Observed

Transmittance (%)

HOMO −0.2179 (a. u)

HF/6-311++G(d,p)

0.1988 (a. u)

LUMO −0.0191 (a. u) B3LYP/6-311++G(d,p)

Fig. 4. Electron density surface plots for the most important frontier molecular orbitals with their energies (a.u.) of 4-(dimethylamino) pyridine (B3LYP).

4000

3500

3000

2500

2000

1500

1000

500

Wavenumber (cm-1) Fig. 2. Observed and simulated IR spectra of 4-(dimethylamino) pyridine.

Observed

[38] assigned CN stretching absorption in the region 1382– 1266 cm1 for the aromatic amines. In benzamide, the band observed at 1368 cm1 is assigned to CN stretching [39]. In the present work, the wavenumbers observed as strong band at 1381 cm1 in FT-IR spectrum and a weak band at 1383 cm1 have been assigned to CN stretching vibration. The other CN vibrations are also identified and presented in Table 2.

Raman intensity

NBO analyses Natural bond orbital analysis gives the accurate possible natural Lewis structure picture of U because all orbitals are mathematically chosen to include the highest possible percentage of the electron density. Interaction between both filled and virtual orbital spaces was correctly explained by the NBO analysis and it could enhance the analysis of intra- and intermolecular interactions. The second-order Fock matrix was carried out to evaluate donor (i)–acceptor (j) i.e. interaction between donor-level bonds and acceptor-level bonds in the NBO analysis [40]. The result of interaction is a loss of occupancy from the concentration of electron NBO of the idealized Lewis structure into an empty non-Lewis orbital. For each donor (i) and acceptor (j), the stabilization energy E(2) associates with the delocalization I ? j is follows:

HF/6-311++G(d,p)

B3LYP/6-311++G(d,p)

Eð2Þ ¼ DEy ¼ qi

3500

3000

2500

2000

1500

1000

500

Wavenumber (cm-1) Fig. 3. Observed and simulated Raman spectra of 4-(dimethylamino) pyridine.

band at 721 cm1 identified in FT-Raman spectrum. The CCC outof-plane bending vibrations of the title compound are well identified in the recorded spectra, within their characteristic region.

CN vibration The identification of CN vibration is a very difficult task, since mixing of several bands are possible in this region. Silverstein et al.

F 2ðijÞ

ej  ei

ð8Þ

where qi is the donor orbital occupancy, ej and ei are diagonal elements and F(i, j) is the off-diagonal NBO Fock matrix element. A natural bond orbital analysis provide an efficient method for studying the intra- and intermolecular bonding and interaction between bonds, and also provides a convenient basis for investigating charge transfer or conjugative interaction in molecular systems. Some electron donor orbital, acceptor orbital, and the interacting stabilization energy resulted from the second-order perturbation theory are reported [41]. The larger the E(2) value the more intensive the interaction between electron donors and electron acceptor, i.e., the more donation tendency from electron donors to electron acceptors and the greater the extent of conjugation of the whole system [42]. Delocalization of electron density between occupied Lewis type (bond or lone pair) NBO orbitals and formally unoccupied (antibond

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V. Balachandran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 277–284 Table 3 Magnetic susceptibility of 4-(dimethylamino) pyridine by B3LYP/6-311++G(d,p). Temperature

Magnetic susceptibility

1/Temperature

50 100 150 200 250 273 298.15 300 350 400 450 500

7.548E07 3.774E07 2.516E07 1.887E07 1.5096E07 1.38242E07 1.26581E07 1.258E07 1.07829E07 9.435E08 8.38667E08 7.548E08

0.02 0.01 0.006667 0.005 0.004 0.003663 0.003354 0.003333 0.002857 0.0025 0.002222 0.002

or Rydgberg) non-Lewis NBO orbital corresponds to a stabilizing donor–acceptor interaction. NBO analysis has been performed on 4DMAP molecule at HF and DFT/B3LYP/6-311++G(d,p) level in order to elucidate the intra-molecular rehybridization and delocalization of electron density within the molecule. The occupancy and hybridization of the various bonding and antibonding orbital are analyzed from the natural bond orbital theory and are presented in Table S2 (Supporting Material). From the Table S2 (Supporting Material) it is observed that the polarization coefficient of the two atoms in antibond is opposite with the opposing polarizations and phases of bond. The bond orbital r(N1C2) and anti bond orbital r⁄(N1C2) of 4DMAP molecule can be displayed as follows

0:7679sp1:82 þ 0:6406sp2:12

rðN1  C2Þ

0:6406sp1:82  0:7679sp2:12

r ðN1  C2Þ

The second-order perturbation theory analysis of Fock matrix in NBO basis of 4DMAP show strong intra-molecular hyper-conjugative interactions of p electrons are given in the Table S3 (Supporting Material). The most important interactions in 4DMAP having lone pair LP (1) N1 with that of r(C2C3) and r(C5C6), results in the stabilization of 11.16 and 11.18 kcal/mol respectively in HF

method. In DFT method the same lone pair interact with r(C2C3) and r(C5C6), results in the stabilization of 9.11 and 9.16 kcal/mol respectively. The lone pair LP (1) N1 interact with r(C3C4) gives the stabilization energy 46.05 and 33.99 kcal/mol in HF and DFT methods, respectively.

Other molecular properties HOMO–LUMO energy gap and related molecular properties The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are very important parameters for quantum chemistry. The HOMO is the orbital that primarily acts as an electron donor while the LUMO is the orbital that largely acts as the electron acceptor [43]. Fig. 4 shows the isodensity plots for the most important frontier molecular orbitals with their energies in (a.u.) of 4DMAP molecule. The HOMO, LUMO and HOMO–LUMO energy gap and quantum chemical parameters of the molecule 4DMAP have been calculated by HF (0.3416 a.u.) and B3LYP (0.1988 a.u.) method with the standard basis set 6-311++G(d,p) and are presented in Table S4 (Supporting Material). The calculated energy gap clearly indicates that the charge transfer takes place within the molecule, which increases molecular activity of the molecule. The isodensity plot of HOMO is localized over the ring and the methyl group, whereas the LUMO picture is localized over the ring only. The quantum chemical parameters are predicted with the HOMO and LUMO orbital energy. Associated within the framework of SCF MO theory the ionization energy and electron affinity can be expressed through HOMO and LUMO orbital energies as I = EHOMO and A = ELUMO. The hardness corresponds to the gap between the HOMO and LUMO orbital energies. The larger the HOMO–LUMO energy gaps the harder the molecule. The global hardness is predicted using the relation g = 1/2(ELUMO  EHOMO). The hardness has been associated with the stability of chemical system. The reciprocal of the hardness will give the softness r = (1/g). The electron affinity can be used in combination with ionization energy

Table 4 Thermodynamic parameters of 4-(dimethylamino) pyridine by HF and B3LYP/6-311++G(d,p). (CP)total (Cal/Mol-Kelvin)

ðH0  E00 Þ=TÞtotal ðCal=Mol-KelvinÞ

ðG0  E00 Þ=TÞtotal ðCal=Mol-KelvinÞ

Stotal (Cal/Mol-Kelvin)

B3LYP/6-311++G(d,p) 100 101.7340 200 104.7011 273 105.7076 298.15 105.9020 300 108.8275 400 113.2900 500 118.5793 600 124.5600 700 131.1175 800 138.1601 900 145.6142 1000 146.2103

14.5033 22.6409 29.4267 31.9166 32.1014 42.0248 50.9874 58.5541 64.8538 70.1289 74.5860 78.3800

10.5831 14.5459 17.5997 18.7021 18.7841 23.3626 28.0136 32.4923 36.6790 40.5401 44.0821 47.3272

53.7193 62.2653 67.2365 68.8352 68.9511 74.9767 80.6910 86.1982 91.5255 96.6791 101.6620 106.4770

64.30245 76.81122 84.83623 87.53724 87.73524 98.33922 108.7046 118.6906 128.2046 137.2191 145.7437 153.8038

HF/6-311++G(d,p) 100 200 273 298.15 300 400 500 600 700 800 900 1000

13.78036 21.23905 27.33195 29.59077 29.75929 39.01894 47.74326 55.33585 61.77652 67.23245 71.88008 75.86252

10.3444 13.9095 16.6671 17.6616 17.7356 21.8983 26.2112 30.4493 34.4774 38.2401 41.72644 44.94596

53.6966 61.9496 66.6799 68.1918 68.3012 73.9671 79.3165 84.4725 89.4720 94.3246 99.0327 103.5980

64.04097 75.8591 83.34706 85.85332 86.03689 95.86536 105.5277 114.9218 123.9495 132.5647 140.7591 148.5439

Temperature (K)

Etotal (kcal/Mol)

108.7111 111.4475 112.3984 112.5885 115.2429 119.3899 124.3546 130.0200 136.2786 143.0410 150.2340 150.8301

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V. Balachandran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 277–284

to give electronic chemical potential, l = 1/2(ELUMO + EHOMO). The global electrophilicity index is x = l2/2g also calculated. Magnetic susceptibility Atoms, molecules, free radicals or ions which contain one or more unpaired electron will posses permanent magnetic dipole moment, that arises from the residual spin and angular momentum of the unpaired electrons. All substances having permanent magnetic moment display paramagnetic behavior in nature. When a paramagnetic substance is placed in a magnetic field, they will align themselves in the direction of the field and thus produces positive magnetic susceptibility, which depends on the temperature; since thermal agitation will oppose the alignment of the magnetic dipoles. The effectiveness of the field diminishes with increase in temperature. The magnetic susceptibility (vm) of the molecules for various temperatures are predicted with knowledge of unpaired electron [44] and presented in Table 3. The graphical representation of (vm) with 1/T (temperature1) is shown in Fig. S2 (Supporting Materials). The effective magnetic moment is found to be a constant, which is 1.7864  105 (BM) and the Curie constant is obtained from the magnetic moment (lm) and is found to be 3.7710  105. Temperature dependence of thermodynamic properties The temperature dependence of the thermodynamic properties namely heat capacity at constant pressure (Cp), thermal energy (E), entropy (S), Gibb’s free energy (G0  E0)/T and enthalpy change (H0  E0)/T) for the compounds 4DMAP were determined by HF/ 6-311++G(d,p) and B3LYP/6-311++G(d,p) method and were listed in Table 4. Fig. S3 (Supporting Materials) (a-e) depicts the correlation of heat capacity at constant pressure (Cp), enthalpy change (H0  E0)/T), Gibb’s free energy (G0  E0)/T, entropy (S), and (E) thermal energy with temperature by HF/6-311++G(d,p) and B3LYP/6-311++G(d,p) method. Table 4 reveals that the entropies, heat capacities, and enthalpy changes are increasing with temperature ranging from 100 to 1000 K due to the fact that the molecular vibrational intensities increases with temperature [45]. The regression factors (R2) of these observed relations of the thermodynamic functions vs. temperatures are all not less than 0.999. For the thermal energy, the regression coefficient (R2) is 0.987. The correlation equations for the thermodynamic parameters with temperature are given in the graphs. These equations are used to predict the value of any thermodynamic parameters for any temperature. Conclusion A complete vibrational analysis of 4DMAP is performed by HF/ 6-311++G(d,p) and B3LYP/6-311++G(d,p) method. The equilibrium geometry of 4DMAP were determined and analyzed both at HF and DFT level of theories utilizing 6-311++G(d,p) basis set. Two different scaling procedures were adopted in this present work. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. It must be due to the fact that hydrogen bond vibrations present in the molecule lead to strong perturbation of the IR wavenumbers and intensities of many other modes. The RMS error of the observed wavenumbers and scaled wavenumbers were discussed. Thermal and magnetic properties of the molecule were analyzed. Quantum chemical parameters were arrived from the frontier molecular orbital theory. The stabilization energies have been calculated from the second-order perturbation theory. Computed wavenumbers were found good agreement with experimental FT-IR and FT-Raman spectra.

Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.saa.2014.01.023. References [1] R.C. Smith, H.H. Emmen, F.W. Bertels Mann, B.M. Kulig, A.C. Van Loenen, C.H. Polman, Neurology 44 (9) (1994) 1701–1705. [2] G.T. Sheeam, N.M.F. Murray, J.C. Rothwell, D.H. Miller, A.J. Thompson, Brain 120 (1997) 299–315. [3] S. Tomaru, S. Matsumoto, T. Kurihara, H. Suzuki, N. Oobara, T. Kaino, Appl. Phys. Lett. 58 (1991) 2583–2585. [4] S.P. Jose, S. Mohan, Spectrochim. Acta A 64 (2006) 240–245. [5] Kirk-Othmer, Encyclopedia of Chemical Technology, fourth ed., John Wiley & Sons, Singapore, 1997. [6] P. Pierrat, P.C. Gros, Y. Fort, J. Comb. Chem. 7 (2005) 879–886. [7] J.H.S. Green, W. Kynaston, H.M. Paisley, Spectrochim. Acta A 19 (1963) 549– 564. [8] V. Sortur, J. Yenagi, J. Tonannavar, Spectrochim. Acta A 69 (2008) 604–611. [9] S. Mohan, R. Murugan, Indian J. Pure Appl. Phys. 30 (1992) 283–290. [10] V. Krishnakumar, R. John Xavier, Spectrochim. Acta A 61 (2005) 253–260. [11] V. Krishnakumar, S. Dheivamalar, R.J. Xavier, V. Balachandran, Spectrochim. Acta A 65 (2006) 147–154. [12] N. Sundaraganesan, S. Ilakiamani, H. Saleem, P.M. Wojciechowski, D. Michalska, Spectrochim. Acta A 61 (2005) 2995–3001. [13] C.S. Hiremath, J. Yenagi, J. Tonannavar, T. Sundius, Spectrochim. Acta A 77 (2010) 918–926. [14] R.N. Medhi, R. Barman, K.C. Medhi, S.S. Jois, Spectrochim. Acta A 56 (2000) 1523–1532. [15] V. Arjunan, A. Suja Ravi Isaac, T. Rani, C.V. Mythili, S. Mohan, Spectrochim. Acta A 78 (2011) 1625–1632. [16] N. Sundaraganesan, B. Dominic Joshua, M. Rajamoorthy, C.H. Gangadhar, Indian J. Pure Appl. Phys. 45 (2007) 967–978. [17] V. Balachandran, A. Lakshmi, A. Janaki, J. Mol. Struct. 1013 (2012) 75–85. [18] V. Arjunan, P.S. Balamourougane, S. Thillai Govindaraja, S. Mohan, J. Mol. Struct. 1018 (2012) 156–170. [19] M.J. Frisch, G.W. Trucks, H.B. Schlegal, G.E. Scuseria, M.A. Robb et al., GAUSSIAN 09, Revision A.02, GAUSSIAN Inc., Wallingford CT, 2009. [20] H.B. Schlegel, J. Comput. Chem. 3 (1982) 214–218. [21] P. Hohenberg, W. Kohn, Phys. Rev. 136 (1964) 864–871. [22] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652. [23] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B37 (1988) 785–789. [24] A. Frisch, A.B. Nielson, A.J. Holder, GAUSSVIEW User Manual, Gaussian Inc., Pittsburgh, PA, 2000. [25] E.D. Glendering, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO Version 3.1. TCI, University of Wisconcin, Madison, 1998. [26] P.L. Polavarapu, J. Phys. Chem. 4 (1990) 8106–8112. [27] G. Keresztury, S. Holly, J. Varga, G. Besenyei, A.V. Wang, J.R. Durig, Spectrochim. Acta A 49 (1993) 2007. [28] G. Keresztury, in: J.M. Chalmers, P.R. Griffiths (Eds.), Handbook of Vibrational Spectroscopy, vol. 1, John Wiley & Sons Ltd., 2002. [29] M.J. Frisch et al., GAUSSIAN 09, Revision A.9, Gaussian, Inc., Pittsburgh, 2009. [30] T. Sundius, MOLVIB, A Program for harmonic Force Field Calculations, QCPE Program NO. 604; T. Sundius, J. Mol. Struct. 218 (1990) 321–326; T. Sundius, Vib. Spectrosc. 29 (2002) 89–95. [31] D.A. Kleinman, Phys. Rev. 126 (1962) 1977–1979. [32] L.M. Sverdlov, M.A. Kovner, E.P. Krainov, Vibrational Spectra of Polyatomic Molecules, Nauka, Moscow, 1970. [33] S.D. Sharma, S. Doraiswamy, Chem. Phys. Lett. 41 (1976) 192–198. [34] G. Socrates, Infrared and Raman Characteristic Wavenumbers, third ed., John Wiley & Sons, Limited, Chichester, 2001. [35] S. Gunasekaran, S. Kumaresan, R. Arunbalaji, S. Srinivasan, J. Chem. Sci. 120 (3) (2008) 315–324. [36] L.J. Bellamy, Infrared Spectra of Complex Molecules, third ed., Wiley, New York, 1975. [37] G. Varsanyi, Assignments for Vibrational Spectra of Seven Hundred Benzene Derivatives, vol. I, Adam Hilger, London, 1974. [38] M. Silverstein, G. Clayton Basseler, C. Morill, Spectrometric Identification of Organic Compounds, Wiley, New York, 1981. [39] R. Shanmugam, D. Sathyanarayana, Spectrochem. Acta A 40 (1984) 764–773. [40] M. Szafran, A. Komasa, E.B. Adamska, J. Mol. Struct. (Thermochem.) 827 (2007) 101–107. [41] C. James, A. Amal Raj, R. Reghunathan, I. Hobert Joe, V.S. Jayakumar, J. Raman Spectrosc. 37 (2006) 1381–1392. [42] S. Sebastian, N. Sundaraganesan, Spectrochim. Acta 75 (2010) 941–952. [43] A.E. Reed, F. Weinhold, J. Chem. Phys. 83 (1985) 1736–1741. [44] M.C. Gupta, Atomic and Molecular Spectroscopy, New Age International (P) Limited, Publishers, New Delhi, 2001. [45] J. Bevan Ott, J. Boerio-Goates, Calculations from Statistical Thermodynamics, Academic Press, 2000.