Molecular structure and vibrational spectra of 2

Indian Journal of Pure & Applied Physics Vol. 47, April 2009, pp. 248-258

Molecular structure and vibrational spectra of 2-chlorobenzoic acid by density functional theory and ab-initio Hartree-Fock calculations N Sundaraganesana, B Dominic Joshuab & T Radjakoumarc a

Department of Physics (Engg.), Annamalai University, Annamalai Nagar 608 002, India Department of Physics, IFET College of Engineering, IFET Nagar, Gangarampalayam, Villupuram 605 108, Tamil Nadu c Department of Physics, KMCPG Studies, Lawspet, Puducherry 605 008 a E-mail: [email protected]

b

Received 15 July 2008; revised 16 December 2008; accepted 3 February 2009 The structure, harmonic frequencies and vibrational mode assignments for 2-chlorobenzoic acid (2CBA) monomer are calculated using HF and DFT methods employing the 6-311++G(d,p) basis set. The results of the molecular structure and vibrational frequencies obtained on the basis of calculations are presented and critically compared with the experimental IR data recorded in gas phase. The Raman and IR spectral data of 2-chlorobenzoic acid (2CBA) obtained in solid phase have also been included. The normal mode analysis has been carried out for all the modes. Most of the modes have wavenumbers in the expected range. The experimental spectra also coincide satisfactorily with those of theoretically constructed spectrograms. Keywords: FTIR, FT-Raman spectra, ab-initio, DFT, 2-chlorobenzoic acid, Vibrational analysis

1 Introduction The derivatives of benzoic acid is an essential component of the vitamin B-complex. Benzoic acid occurs widely in plants and animals tissues along with vitamin B-complex and is used in miticides, contrast media in urology, cholocystographic examinations and in the manufacture of pharmaceuticals. Because of its wide applications, the surface enhanced Raman scattering studies1, vibrational spectra of benzoic acid2 and nitro derivatives have been extensively investigated. The CAS number of the compound 2chlorobenzoic acid is 118-91-2. Arthur et al3. recorded and studied the IR and Raman spectra of p-, m-, and o-chlorobenzoic acids (CBAs) in solid form and in different solutions. Vibrational assignments have been proposed based essentially on group frequency, band shape, intensity and some internal consistency of CBAs. Examinations of the carboxylic acid and the carboxylate vibrations show that chlorobenzoic acids (CBA's) exist as hydrogen-bonded dimers in solid and monomeric acids in organic solvents such as diethyl ether, chloroform and ethanol, while existing as carboxylate ions in sodium hydroxide solutions. Sánchez et al.4 have studied the use of a semiempirical method based on the application of group theory to a previously established geometrical model according to the molecular structure allowed to carry

out the vibrational analysis of infrared and Raman spectra in solid phase of some o-substituted benzoic acid derivatives. Because of the effect of the different substituents on the frequency of the ring vibrational normal modes is slight, the study of the ring vibrations independently of the substituent internal vibrations was possible. On this basis, a tentative assignment of the ring vibrational normal modes for the o-NH2, o-CH3, oCl and o-COOH benzoic acids is proposed. Yesook Kim et al5. have investigated the isotopically consistent assignments of the IR and Raman bands of benzoic acid, benzoic-d5 acid, benzoic-p-d acid and their —COOD analogues are given on the basis of a normal coordinate analysis for the vibrational modes in the crystalline state. The IR spectra of the six isotopic benzoic acids were simulated by using the calculated normal modes and a simple charge flux model. Durig6 resolved multiplet structure of carboxylic ring bands observed for benzoic acid and d5-deuterated benzoic acid by IR and Raman spectroscopy at low temperatures, is not in agreement with previous assignments. The temperature dependence of halfwidths of some other vibrational bands reveals that more than one mechanism for proton-pair disorder has to be taken into account. Recently, we have also carried FTIR and FT-Raman spectra, assignments and ab-initio calculations of 5-amino-2-chlorobenzoic acid7 and 2amino-4,5-difluorobenzoic acid8.

SUNDARAGANESAN et al.: VIBRATIONAL SPECTRA OF 2-CHLOROBENZOIC ACID

The vibrational spectra of 2-chlorobenzoic acid (2CBA) molecule have been studied 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. Density functional theory calculations are reported to provide excellent vibrational frequencies of organic compounds if the calculated frequencies are scaled to compensate for the approximate treatment of electron correlation, for basis set deficiencies and the anharmonicity9-14. 2 Experimental Details The compound 2CBA in the solid form was purchased from the Sigma−1 Aldrich Chemical Company

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(USA) with a stated purity of greater than 99% and it was used as such without further purification. The gas phase infrared spectrum of 2-chlorobenzoic acid was measured in the range 5000-500 cm-1 with a resolution of 0.5 cm-1. The FT-Raman spectrum of 2CBA has been recorded using 1064 nm line of Nd:YAG laser as excitation wavelength in the region 100-4000 cm−1 on a Brucker model IFS 66 V spectrophotometer equipped with FRA 106 FT-Raman module accessory. The FT-IR spectrum of this compound was recorded in the region 400-4000 cm-1 on IFS 66 V spectrophotometer using KBr pellet technique. The observed experimental FT-IR (solid and gas phase), FT-Raman and scaled IR spectra are shown in Figs 1-4. The spectral measurements were carried out at Sophisticated Analytical Instrumentation Facility (SAIF), IIT, Chennai.

Fig.1 FT-IR solid phase spectrum of 2-chlorobenzoic acid

Fig.2 FT-IR gas phase spectrum of 2-chlorobenzoic acid

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3 Computational Details All calculations were performed at Hartree-Fock (HF) and B3LYP levels on a Pentium IV/3.02 GHz personal computer using Gaussian15 03W program package, invoking gradient geometry optimization16. Initial geometry generated from standard geometrical parameters was minimized without any constraint in

the potential energy surface at Hartree-Fock level, adopting the standard 6-31G(d,p) basis set. This geometry was then re-optimized again at HF and the gradient corrected density functional theory17 (DFT) with the Becke’s three parameter hybrid functional18 (B3) for the exchange part and the Lee-Yang-Parr (LYP) correlation function19, accepted as a cost

Fig.3 Experimental FT-Raman spectrum of 2-chlorobenzoic acid

Fig.4 (a) Experimental FT-IR spectrum of 2-chlorobenzoic acid (b) Scaled IR spectrum of 2-chlorobenzoic acid

SUNDARAGANESAN et al.: VIBRATIONAL SPECTRA OF 2-CHLOROBENZOIC ACID

effective approach20, for the computation of molecular structure, vibrational frequencies and energies of optimized structures. All the computations have been done by adding polarization function d and diffuse function on heavy atoms21 and polarization function p and diffuse function on hydrogen atoms22, in addition to triple split valence basis set [6-311++G(d,p)], for better treatment of polar bonds of chloro and carboxyl groups. The optimized structural parameters were used in the vibrational frequency calculations at the HF and DFT levels to characterize all stationary points as minima. The vibrational frequencies computed at DFT level have been adjudicated to be more reliable than those obtained by the computationally demanding Moller-Plesset perturbation methods23. The density functional theory offers electron correlation frequently comparable to second-order Moller-Plesset theory (MP2). Finally, the calculated normal mode vibrational frequencies provide thermodynamic properties also through the principle of statistical mechanics. By combining the results of the GAUSSVIEW program24 with symmetry considerations, alongwith available related molecules, vibrational frequency assignments were made with a high degree of accuracy. 4 Results and Discussion 4.1. Molecular Geometry

The labelling of atoms in 2-chlorobenzoic acid is shown in Fig. 5. The optimized geometrical parameters (bond length and angles) by HF, DFT/B3LYP with 6311++G(d,p) as basis set are presented in Table 1. It compares the calculated bond lengths and angles for 2CBA with those of experimentally available from X-

Fig.5  Numbering (2- chlorobenzoic acid)

system

adopted

in

this

study

251

ray data for 2-chlorobenzoic acid26. The geometric structure is monoclinic, the space group C2/c with the cell dimensions: a = 14.73 ±.0.03, b = 3.90 ± 0.02, c = 25.50 ± 0.05 Å and β = 112°40′ ± 20′. From the theoretical values, we find that most of the optimized bond lengths are slightly shorter as well as longer than the experimental value at HF and B3LYP levels due to the theoretical calculation belong to isolated molecules in gaseous phase and the experimental results belong to molecule in solid state. Comparing bond angles and bond lengths of HF and B3LYP as a whole the B3LYP calculated value correlates well compared with experimental results. As expected, the geometrical parameters of 2CBA presented in Table 1 vary with the method used in calculations The effect of the substituents on the phenyl ring seems to be interesting. The benzene ring appears to be little distorted with C1-C2 and C1-C6 bond lengths exactly at the substitution place ∼ 1.40 Å longer than the remaining bonds C2-C3 (C5-C6), C3-C4 (C4-C5) (∼ 1.39 Å). The increase of the C-C bond lengths exactly at the substitution place C1-C2 (C1-C6) is accompanied by slightly irregular hexagonal structure of the angles C2-C1-C6 and C1-C2-C3, 118.0° and 120.5°, respectively at the B3LYP/6-311++G(d,p). This is in accordance with the experimental results. The density functional calculation gives shortening of the angle C6C1-C12 by 5.0° and increase of the angle C2-C1-C12 by 7.0° from 120° at the C1 position and this asymmetry of exocyclic angles reveals the repulsion between the COOH group and the phenyl ring. The asymmetry of the exocyclic angles C1-C2-Cl11 and C3-C2-Cl11 is less at the C2 position, which gives less repulsion of Cl group with the carboxylic oxygen atom. The computed values of above angles correlate well with the X-ray data. The C-Cl bond length is found 1.754 Å (B3LYP). 1.741 Å (HF). Akyuz et al.27 also calculated this bond length 1.746 Å for 3-chloropyridine and 1.748 Å for 2-chloropyridine28 by using force field calculations. These bond length was also observed to be 1.744, 1.744, 1.739 (Ref.29) and 1.735 Å(Ref.30) for N-2-(4,6lutidiyl)-N’-chloro phenylthioureas (4,6 LutTu2Cl, 4,6 LutTu3Cl and 4,6 LutTu4Cl) and 3-chloro-5-hydroxy, 2,6-dimethylpyridine, respectively. Many researchers31-35 explained the changes in frequency or bond length of the C-H bond on substitution due to a change in the charge distribution on the carbon atom of the benzene ring. The substituents may be of the electron withdrawing type (Cl, F, Br etc). The carbon atoms are bonded to the

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INDIAN J PURE & APPL PHYS, VOL 47, APRIL 2009 Table 1  Geometrical parameters optimized in 2-chlorobenzoic acid, bond length (Å) and angle (°) HF/6-311++G(d,p)

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

XRD a 2-chlorobenzoic acid

C1-C2 C1-C6 C1-C12 C2-C3 C2-Cl11 C3-C4 C3-H7 C4-C5 C4-H8 C5-C6 C5-H9 C6-H10 C12-O13 C12-O14 O14-H15 Bondangle (°)

1.392 1.393 1.498 1.385 1.741 1.382 1.073 1.384 1.075 1.380 1.074 1.073 1.185 1.320 0.946

1.405 1.404 1.496 1.395 1.754 1.390 1.082 1.394 1.084 1.387 1.083 1.083 1.209 1.348 0.969

1.405 1.365 1.521 1.386 1.737 1.386 --1.362 --1.407 ----1.208 1.295 ---

C2-C1-C6 C2-C1-C12 C6-C1-C12 C1-C2-C3 C1-C2-Cl11 C3-C2-Cl11 C2-C3-C4 C2-C3-H7 C4-C3-H7 C3-C4-C5 C3-C4-H8 C5-C4-H8 C4-C5-C6 C4-C5-H9 C6-C5-H9 C1-C6-C5 C1-C6-H10 C5-C6-H10 C1-C12-O13 C1-C12-O14 O13-C12-O14 C12-O14-H15 a Taken from Ref. [33]

118.4 126.4 115.2 120.4 123.0 116.5 120.2 119.2 120.6 120.2 119.4 120.4 119.4 120.6 120.1 121.4 118.1 120.4 122.7 114.7 122.5 108.5

118.0 127.0 115.0 120.5 123.2 116.2 120.3 119.0 120.6 120.1 119.4 120.5 119.4 120.5 120.0 121.7 117.5 120.8 123.2 114.6 122.2 106.6

120.5 122.5 117.0 119.0 124.7 116.3 120.6 ---119.8 ----120.7 ----119.5 ----122.2 113.3 124.5 ---

Parameters Bond length (Å)

hydrogen atoms with a σ bond in benzene and the substitution of a halogen for a hydrogen reduces the electron density at the ring carbon atom. The ring carbon atoms in substituted benzenes exert a larger attraction on the valence electron cloud of the hydrogen atom resulting in an increase in the C-H force constance and a decrease in the corresponding bond length.

4.2 Vibrational assignments

According to the theoretical calculations, 2CBA has a planar structure of Cs point group symmetry. The molecule has 15 atoms and 39 normal modes of fundamental vibrations which span the irreduciable representations: 27A′ + 12A″. All the 39 fundamental vibrations are active in both IR and Raman. The

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assignments are presented in Table 2 for several of phenyl ring modes along with substituents are briefly given in the present work. The harmonic-vibrational frequencies calculated for 2CBA at HF and B3LYP levels using the triple split valence basis set 6-311++G(d,p) have been presented in Table 2. The observed FTIR and FTRaman frequencies for various modes of vibrations are also presented in Table 2. The comparison of the frequencies calculated at HF and B3LYP with experimental values (Table 2) reveals the over estimation of the calculated vibrational modes due to neglect of anharmonicity in real system. The inclusion of electron correlation in density functional theory to a certain extend makes the frequency values smaller in comparison with the HF frequency data. Anyway not withstanding the level of calculations, it is customary to scale down the calculated harmonic frequencies in order to improve the agreement with the experiment. The frequencies of CH and OH stretching and bending vibrations were scaled by 0.958 (derived from the recently reported scaling factor for the valence A-H stretching force constant36). The other harmonic frequencies below 2000 cm-1 were scaled by the factor of 0.983 determined in previous studies of similar organic systems37. The mean absolute deviation, standard deviation (SD), root mean square value and correlation coefficient (r) between the calculated harmonic and observed fundamental vibrational frequencies for each method and 6-311++G(d,p) basis set was also calculated in order to investigate the performance and vibrational frequencies for the title molecule. The root mean square (RMS) values were obtained in this study using the following expression25. 1 RMS= N −1

N

∑

(vi

cal

− vi

exp 2

)

i =1

These results are given in Table 3, indicate that the fundamental frequencies calculated (DFT) for the title compound show quite good agreement with the experimental values. Furthermore, the 6-311++G(d,p) basis set calculation approximates the observed fundamental frequencies much better than other basis set results. The frequency values computed at the RHF level contain known systematic error due to the negligence

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Table 3Mean absolute deviation, standard deviation (SD), correlation coefficient (r) and root mean square between the calculated and observed fundamental vibrational frequencies of the title compound Parameters

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

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

Mean absolute deviation S.D. RMS r

40.7407 40.6052 57.5203 0.9990

39.4074 31.2792 51.2708 0.9995

Table 4Theoretically computed total energies (a u), zero-point vibrational energies (kcal mol-1), rotational constants (GHz), entropies (cal mol-1 K-1) and dipole moment (D) for 2-chlorobenzoic acid Parameters Total energy Zero-point energy

HF

B3LYP

6-31G(d,p)

6-311++G(d,p)

6-31G(d,p)

6-311++G(d,p)

-877.2259741 71.68

-877.3456395 71.11

-880.4192557 66.54

-880.5607311 66.14

1.4908 1.1907 0.6792

1.4972 1.1858 0.6830

1.4525 1.1939 0.6563

1.4674 1.1809 0.6676

90.153 41.044 29.968 19.142 2.133

90.382 41.044 29.962 19.377 2.176

94.325 41.044 30.025 23.256 1.728

92.473 41.044 30.009 21.420 2.103

Rotational constants

Entropy Total Translational Rotational Vibrational Dipole moment

of electron correlation. Therefore, a linearity between the experimental and calculated wavenumbers (i.e. for the whole spectral range considered), can be estimated by plotting the calculated versus experimental wavenumbers (Fig. 6). Certain wavenumbers obtained between the two methods, are strongly underestimated. As seen in Fig. 6, if these variations are omitted, ab-initio calculations and DFT/B3LYP calculations provide good linearity between the calculated and experimental wavenumbers (correlation coefficients of HF and DFT/B3LYP are 0.9990 and 0.9995, respectively). 4.3 C-H vibrations

Fig.6 Graphic correlation between the experimental and calculated wavenumber obtained by the ab-initio HF and DFT/B3LYP/6-311++G(d,p) methods for 2- chlorobenzoic acid

There are four (7a, 7b, 20 and 20b) stretching vibrations in di-substituted benzenes whose wavenumbers38 fall in the range 3100-3000 cm-1. In this region, the bands are not affected appreciably by the nature of substituents. The C-H stretching modes usually appear with strong Raman intensity and are highly polarized. May be owing to this high polarization, Raman bands have not been observed in experimental spectra. The 2-chlorbenzoic acid molecule gives rise to four C-H stretching, four C-H in-plane bending vibrations and four C-H out-of-plane

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bending vibrations. Since 2CBA is a di-substituted aromatic system, it has four adjacent C-H moieties. The expected four C-H stretching vibrations correspond to stretching modes of C4-H, C5-H, C3-H and C6-H units. The vibrations mode nos. 2-5 assigned to aromatic C-H stretch39 in the region 3042-3072 cm-1 are in agreement with experimental assignment40 3026-3093 cm-1. These frequencies show good agreement with B3LYP method. The C-H in-plane bending vibrations assigned in the region 1263-1110 cm-1 even though found to be contaminated by CO stretching and OH in-plane bending are in the range found in literature18,19, while the experimental observations are at 1255-1103 cm-1. The scaled frequencies 796-989 cm-1 for the C-H outof-plane bending falls in the FT-Raman values of 809-950 cm-1. 4.4 C-C vibrations

Out of the six ring stretching modes, the two modes (8a and 8b) and (19a and 19b) appears in very narrow spectral ranges 1625–1570 and 1425–1470 cm-1, respectively, in disubstituted benzene derivatives. The actual positions are determined not so much by the nature but by the position of the substituents around the ring. The degenerate vibrational pair 8 of the phenyl ring splits and 8a possesses higher wavenumbers. The bands observed at 1430, 1466, 1569 and 1589 cm-1 of 2-chlorobenzoic acid are identified as C-C stretching vibrations. The theoretically calculated C-C stretching vibrations by B3LYP/6-311++G (d, p) are at 1440, 1474, 1575 and 1604 cm-1 show excellent agreement with recorded spectral data. The computations predict the band for 19a and 19b at 1575 cm-1 and 1474 cm-1, respectively. The C-C aromatic stretch, known as semi-circle stretching, predicted at 1575 cm-1 is also in excellent agreement with experimental observations of 1569 cm-1 in FTIR spectrum. All the experimental and calculated frequencies agree well with the observed data. In the benzene, fundamental (992 cm-1) and (1010 cm-1) represent the ring breathing mode (mode 1) and carbon trigonal bending mode. Under the Cs point group, both the vibrations are very close, there is an appreciable interaction between these vibrations and consequently their energies will be modified. The ring breathing and trigonal bending modes of 2CBA are assigned 1050 and 997 cm-1, respectively41. The theoretically scaled values at 1042 and 1039 cm-1 by B3LYP/6-311++G (d, p) method coincides with experimental observations.

4.5 C-Cl vibrations

The vibrations belonging to the bond between the ring and halogen atoms are worth to discuss here since mixing of vibrations are possible due to the lowering of the molecular symmetry and the presence of heavy atoms on the periphery of the molecule19. The assignments of C-Cl stretching and deformation vibrations have been made by comparison with similar molecules, p-bromophenol42 and the halogensubstituted benzene derivatives39. Mooney43,44 assigned vibrations of C-X group (X=Cl, Br, I) in the frequency range 1129-480 cm-1. The C-Cl stretching vibrations give, generally, strong bands in the region 710-505 cm-1. Compounds with more than one chlorine atom exhibit very strong bands due to the asymmetric and symmetric stretching modes. Vibrational coupling with other groups may result in a shift in the absorption to as high as 840 cm-1. For simple organic chlorine compounds, C-Cl absorptions are in the region 750-700 cm-1, whereas for the transand gauche- forms45 they are near 650 cm-1. In the FTIR spectrum of 2CBA, the medium band at 454 cm-1 in FTIR spectrum and a medium band at 456 cm-1 in FT-Raman spectrum, respectively are assigned to C-Cl stretching vibration. The theoretical calculation by B3LYP/6-311++G(d,p) method at 446 cm-1 exactly correlates with experimental observation. The C-Cl in-plane bending and out-of-plane bending vibrations are assigned to the Raman bands at 303 cm-1 and 216 cm-1, respectively. This is in agreement with the literature data46,47,39. 4.6 COOH vibrations

Bands due to OH stretching vibrations, ν (OH), are much more intense in IR than Raman spectra48. When carboxylic groups form hydrogen bonding, the result is a broad band centered at 2900-3100 cm-1, that superimposes ν (C-H) band(s). However, in our title molecule a medium band observed at 3581 cm-1 in gas phase has its origin in the O-H stretching vibration. The scaled wavenumber by B3LYP/6-311++G(d,p) method at 3599 cm-1 shows very good agreement with experimental observations. The most characteristic feature of carboxylic group is a single band usually in the range 1700-1800 cm-1. This band is due to the C=O stretching vibration, v(C=O). In the solid state, most of carboxylic acids form a dimeric structure that is due to the result of hydrogen bonding between two neighbouring -COOH groups. In such a case, two v(C=O) are expected, one

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that is Raman active (in-phase, symmetric stretching vibration) and the other one, out-of-phase (antisymmetric stretching vibration), is IR active only. The band appearing at 1698 cm−1 is assigned as C=O stretching vibration in FTIR spectrum. However, the gas phase spectrum for the same vibrations show at 1767 cm-1 as a very strong band. The theoretically computed value of 1746 cm-1 shows very good agreement with FTIR gas phase experimental results. Two other characteristic carboxylic group vibrations are; C-O stretching v(C-O), and in-plane C-O-H bending, β(C-OH). They are expected in the 1150-1450 cm-1 region depending on whether monomeric, dimeric or other hydrogen bonded species are present48,49. Generally, the v(C-O) mode appears at higher frequency than the β(C-OH) mode. However, these bands overlap with other bands that are due to aromatic or aliphatic chain vibrations causing that their undisputed assignment is very difficult. Thus, they can be easily found from the spectra with the help of theoretical calculations. Based on the above facts, a strong band at 1327 cm-1 in FTIR and medium band at 1328 cm-1 in FTIR gas phase is assigned to C-O stretching vibration. For the β(C-OH) bending vibration a medium strong band at 1188 cm-1 in FT-Raman is the correct choice having no error. The scaled wavenumber by B3LYP/6311++G(d,p) predicts at 1351 and 1189 cm−1, respectively for the v(C-O) and β(C-OH) vibrations, respectively. The C-OH out-of-plane bending vibration observed as very weak band in FT-Raman at 610 cm-1. The scaled vibration at 614 cm-1 by HF/6311++G(d,p) shows excellent agreement with experimental observations.

5 Other Molecular Properties Several calculated thermodynamic parameters and the computed statistical values are presented in Table 4. Scale factors have been recommended51 for an accurate prediction in determining the zero-point vibration energies (ZPVE), and the entropy, Svib(T). The variations in the ZPVEs seem to be insignificant. The total energies are found to decrease with increase of the basis set dimension. The change in the total entropy of 2CBA at room temperature at different basis sets are only marginal. The total energies and the change in the total entropy of 2CBA at room temperature at different methods are also presented.

4.7 C-COOH vibrations

References

In 2-chlorobenzoic acid, the strong band at 1278 cm-1 in FT-Raman spectrum corresponds to CCOOH stretching vibrations. The scaled value of 1298 cm-1 by B3LYP/6-311++G(d,p) coincides very well with experimental observation. The bands at 151 and 81 cm-1 in Raman spectrum is assigned to C-COOH in-plane and out-of-plane bending, respectively. The scaled values (195 and 112 cm-1) of above said vibrations are not in agreement with experimental observation. The former result is in good agreement with earlier work50. However, the torsion vibration of -COOH group predicted at 34 cm-1 by B3LYP/6-311++G(d,p) method is missing in both FTIR and FT-Raman experimental observation.

6 Conclusions The FTIR (gas phase), FTIR and FT-Raman (solid phase) have been recorded and the detailed vibrational assignments are presented for 2CBA for the first time. The harmonic-vibrational frequencies, IR intensities, Raman scattering activities and IR spectra of 2CBA were determined and analysed both at HF and DFT B3LYP/6-311++G(d,p) levels of theory. The difference between the corresponding wavenumbers (observed and calculated) is very small, for most of the fundamentals. Therefore, the results presented in this work for 2CBA indicate that this level of theory is reliable for prediction of both infrared and Raman spectra of the title molecule. The optimized geometry parameters calculated at B3LYP/6-311++G(d,p) and HF/6-311++G(d,p) are slightly shorter as well as longer than experimental values and the B3LYP calculated values coincides well compared with the experimental data on the whole. 1 Shou-Yih Wang, Chen-Yuan Chou & Liang N T, J Raman Spectrosc 19 (1988) 365. 2 Kresimir Furic & James R Durig, Chem Phys Lett 126 (1986) 92. 3 Arthur S Lee L & Ying-Sing Li, Spectrochim Acta 52A (1996) 173. 4 Sánchez E de la ßlanca, Núñez J L & Martinez P, J Mol Struct, 142 (1986) 45. 5 Yesook Kim & Katsunosuke Machinda, Spectrochim Acta, 42A (1986) 881. 6 James R Durig, Chem Phy Lett, 126 (1986) 92. 7 Sundaraganesan N, Dominic Joshua B & Settu K, Spectrochim Acta, 66A (2007) 381. 8 Sundaraganesan N, Ilakiamani S & Dominic Joshua B, Spectrochim Acta, 67A (2007) 287. 9 Handy N C, Maslen P E, Amos R D, Andrews J S, Murry C W & Laming G, Chem Phys Lett, 197 (1992) 506.

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