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N.Jayamania*, N.Geethab
a* Department of Physics, Vivekanandha College of Arts & Sciences(W), Namakkal-637205, India
b Department of Physics, Bharathiyar Arts&Science College (W), Salem-636112, India
_______________________________________________________________________________________________
A solid phase FTIR and FT-Raman spectra of p-bromo benzoic acid (p- BBA) and p-fluoro benzoic acid (p-FBA) were recorded in the region 4000-
400cm-1 and 4000-50cm-1 respectively. The spectra were interpreted with the aid
of normal coordinate analysis following full structure optimization and force field calculations based of DFT using standard B3LYP/6-31G** basis set combination and was scaled using various scale factors yielding fairly good agreement between observed and calculated frequencies. The effects of bromo and fluoro substitutions on the structure and vibrational requencies have been investigated. The Infrared and Raman spectra were also predicted from the calculated intensities.
Keywords: p-bromo benzoic acid and p-fluoro benzoic acid; Density functional
theory; FTIR spectroscopy; FT-Raman spectroscopy; Vibrational spectra;
*Correspondence to: N. Jayamani, Department of Physics, Vivekanandha
College of Arts & Sciences(W), Namakkal-637205, India
E-mail: njayamaniravi@yahoo.co.in
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Vibrational spectroscopy is used extensively in organic chemistry, for the identification of functional groups of organic compounds, for studies on molecular conformation and reaction kinetics, etc. Due to the great biological and pharmaceutical importance, the vibrational studies of p-BBA and p-FBA have been carried out in this present investigation. The aromatic acids are crystalline substance, generally slightly soluble in water and well soluble in organic solvents like alcohol, chloroform, and benzene etc. One of the most common uses of benzoic acid is food preservatives [1]. It is also used in the manufacture of artificial flavors and perfumes and for the flavoring of tobacco. In medicine, the benzoic acid is used as an anti-microbial agent [2]. Benzoic acid and its derivatives inhibit the growth of mold, yeast and some bacteria [3]. Benzoic acid is found in toothpastes and mouthwashes, cosmetics and deodorants. In the present investigation, a complete study of vibrational spectra of p-BBA and p- FBA has been carried out. The fluorine and bromine substituent’s present in the title compounds are highly electronegative and hence they withdraw the electrons from the ring, which results into the change in ionization potential, electronic affinity and excitation energies of the systems.
Quantum chemical computational methods have proven to be an essential tool for interpreting and predicting the vibrational spectra [4, 5]. In the SQM approach the systematic errors of the completed harmonic force field are corrected by a few scale factors which are found to be well transferable between
chemically related molecules [5-7]. The vibrational analysis of p-BBA and p-FBA
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using the SQM force field method based of DFT calculation has been presented [8]. The calculated infrared and Raman spectra of the title compounds are also simulated utilizing the scaled force fields and the computed dipole derivatives for IR intensities and polarizability derivatives for Raman intensities.
The fine crystalline samples of p-BBA and p-FBA were obtained from Lancaster chemical company, UK and used as such for the spectral measurements. The Fourier transform infrared spectrum of the title compounds were recorded in the region 400–4000 cm-1 using Perkin-Elmer spectrum RXI spectrophotometer equipped with He-Ne laser source, KBr beam splitter and LiTaO3 detector. The samples were prepared by pressing p-BBA and p-FBA with KBr into pellet form.
The FT-Raman spectra of p-BBA and p-FBA were recorded on a BRUKER IFS–66V model interferometer equipped with an FRA-106 FT-Raman accessory in the 4000-50 cm-1 Stokes region using the 1064 nm line of a Nd:YAG laser for excitation operating at 200mW power. The reported frequencies’ are believed to be accurate within ± 1 cm-1.
Quantum chemical density functional calculations were carried out with the GAUSSIAN 98 W Program [9], using the Becke3-Lee-Yang-Parr (B3LYP) functional supplemented with the standard 6-31G** basis set (referred to as DFT calculations) [10,11]. The Cartesian representation of the theoretical force constants have been computed at the fully optimized geometry by assuming CS
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point group symmetry. The multiple scaling of the force constants were performed by the quantum chemical method with selective scaling in the local symmetry coordinate representation [12], using transferable scale factors available in the literature [13]. The transformation of force field from Cartesian to symmetry coordinate, the scaling, the subsequent normal coordinate analysis, calculation of potential energy distribution (PED) and IR and Raman intensities were done on a PC with the version V7.0-G77 of the MOLVIB program written by Sundius [14, 15]. To achieve a close agreement between observed and calculated wave numbers, the least square fit refinement algorithm was used. For the plots of simulated IR and Raman spectra, pure Lorentzian band shapes
were used with a bandwidth (FWHM) of 10 cm-1.
The Raman activities (Si) calculated by the GAUSSIAN 98 W program and adjusted during the scaling procedure with MOLVIB were converted to relative Raman intensities (li) using the following relationship derived from the basic theory of Raman scattering [16-18].
I i =
f (υo − υi ) Si
(1)
− hcυ
υ 1 − exp i
KT
Where, υ0 is the exciting frequencies (in cm-1 units). υi is the vibrational frequencies of the ith normal mode, h, c and k are the universal constants and ƒ
is a suitably chosen common normalization factor for all peak intensities.
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The molecular structures of p-BBA and p-FBA having cs symmetry are shown in Figs. 1(a) &1(b), respectively. The global minimum obtained by the DFT structure optimization for p-BBA and p-FBA are calculated as -2991.9382
Hartrees and -520.0677 Hartrees, respectively.
The energy difference is clearly understandable, since the environments of the molecules are different. The calculated optimized geometrical parameters obtained in this study for p--BBA and p-FBA are presented in Table 1. All vibrational frequencies have been calculated and they were found to be positive.
The output of the quantum-mechanical calculations contains the force constants matrix in Cartesian coordinates and in Hartrees/Bhor2 units. These force constants were transformed to the force fields in the internal local symmetry coordinates; defined interims of the internal valence coordinates following the IUPAC recommendations [19, 20] are given in Table2 for p-BBA and p-FBA. The force fields determined were used to calculate the potential energy distribution (PED) among the normal coordinates.
The bonding properties of the title compounds are influenced by the rearrangements of electrons during substitutions and addition reactions. The values of the stretching force constants between carbon and bromine atoms of p- BBA are found to be lesser than the corresponding values between carbon and
fluorine atoms of p-FBA because of fluorine atom which has higher
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electronegative than bromine. The force constant of a bond increases numerically with bond order and consequently decreases with the increase in bond length. The stretching force constant of C=O is greater than C-O.
The 39 normal modes of p-BBA and p-FBA are distributed amongst the symmetry species as
r vib =27A ‘ (in-plane) + 12 A” (out- of- plane)
and in agreement with Cs symmetry, all the vibrations are active both in the Raman scattering and Infrared absorption. The detailed vibrational assignments of fundamental modes of p-BBA and p-FBA along with the observed and calculated frequencies, IR and Raman intensities and normal mode descriptions (characterized by PED) are reported in Tables 3&4. For visual comparison, the observed and simulated FTIR and FT-Raman spectra of p-BBA and p-FBA are presented in Figs 2-5 respectively. Root mean square (RMS) values were obtained in this study using the following expression
RMS =
1
(n − 1)
∑ (υ
i
calc i
− υ exp )2
(2)
The harmonic frequencies (DFT-calculated) were found to be 10-15% more than that of the experimentally obtained frequencies (anharmonic). All vibrational assignments are based on the respective point group symmetry for each molecule.
Assignments were made through visualization of the atomic displacement
representations for each vibration, viewed through GAUSSVIEW [21] and
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matching the predicted normal frequencies and intensities with experimental data. It is convenient to discuss the vibrational spectra of p-BBA and p-FBA in terms of characteristic spectral regions as described below.
Aromatic system exhibits the C-H stretching vibrations in the region 3100-
3000 cm-1. In the present study, the C-H vibrations of the title compounds are observed at 3092, 3068, 3045 cm-1 for p-BBA 3084,2997,2952 cm-1 in the FTIR spectra. The bands observed at 3076 cm-1 for p-BBA and 3094, 3078 cm-1 for p- FBA in FT-Raman spectrum are assigned to C-H stretching vibration. The bands due to C-H in-plane bending vibration interacting some what with C-C stretching vibration are observed as a number of weak to medium intensity sharp bands in the region1300-1000 cm-1. The C-H out-of plane bending vibrations give rise to intense bands in the region 900-667 cm-1 [22]. The C-H in-plane and out-of-plane bending vibrations for the title compounds are found to be well with in the characteristic region which are depicted in tables 3&4.
Due to the presence of strong intermolecular hydrogen bonding, carboxylic acid normally exists as dimer. Their spectra exhibit a broad band due to the O-H stretching vibration and a strong band due to C=O stretching vibration. In the presence of hydrogen bonding, carboxylic acids in the liquid and solid phases exhibit a broad band at 3300 to 2500 cm-1, due to the O-H stretching vibrations [23, 24]. In the present study, the bands identified at 3092 cm-1 for p-BBA and
3094 cm-1 for p-FBA are assigned to O-H stretching vibrations. The C=O
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stretching bands of carboxylic acids are considerably more intense than kenotic C-O stretching bands. The characteristics infrared absorption wavenumbers of C=O in acids are normally strong in intensity and found in the region 1800-1690 cm-1 [25-27]. In the case of dimers (solid or pure liquid state) strong hydrogen bonding and resonance lower the force constants of the C=O bond thus resulting in the absorption of C=O group at a lower frequencies (1720-1680 cm-1). The C=O formed by Pπ - Pπ bonding between C and O[28,29]. Internal hydrogen bonding reduces the frequency of the C=O stretching absorption to a greater degree than does intermolecular hydrogen bonding because of the different electro-negativities of C and O, the bonding are not equally distributed between the two atoms. The lone pair of electrons on oxygen also determines the nature of carbonyl groups. In this study, the FTIR band observed at 1692 cm-1 in p-BBA
and 1687cm-1 in p-FBA are assigned to C=O stretching vibrations.
The C-O-H in-plane bending appears as a weak band near 1420 cm-1 and C- O stretching as a more intense band near 1300 cm-1. Since both the bands involve some interaction between them, they are referred to as coupled O-H in- plane bending and C-O stretching vibrations. This is also confirmed by PED output results from tables1&2.Tthe C-O stretching vibrations are assigned to
1134 cm-1 in FT-Raman for p-BBA and 1096 cm-1 in FTIR spectra for p-FBA. The in-plane bending and out-of-plane bending vibrations have been identified and presented in Tables 3&4.
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The stretching vibrations of bromine compound have strong absorptions at
650- 395 cm-1. In the present study, the C-Br stretching vibration of p-BBA has been observed at 437 cm-1. The in-plane and out-of-plane bending vibrational assignments of C-Br are shown in Table 3. These assignments are in good agreement with the literature [30].
Aromatic fluoro compounds have medium intensity bands in the region 1270-
1100 cm-1, those with only one fluorine atom on the ring tending to absorb at
1230 cm-1 [30]. In the present study, a weak band observed in FTIR spectrum at
1237 cm-1 is assigned to C-F stretching vibrational mode of p-FBA. The C-F in- plane bending and out-of-plane bending vibrations have been identified and presented in Table 4.
The ring stretching, in-plane and out-of-plane bending vibrations have been identified and presented in Tables 3&4. They are also supported by literature [31,
32].
A complete vibrational analysis of the title compounds were performed based on the SQM force field obtained by DFT calculations at B3LYP/6-31G** level. The assignments of all the fundamentals were made unambiguously, taking advantage of FTIR and FT-Raman experimental data as well as effective scaling and the IR intensity information from DFT. The bromine and fluorine
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substituents in the benzoic acid structure produce a remarkable effect on the geometry and spectroscopic proprieties of the title compounds. The –I > +M effect of the bromine and fluorine acted not only in the close environment of the place of the substitution but also on other parts of the ring through π-electron system. As a result of the halogen atoms substituents in the ring , remarkable changes are observed.
Acknowledgement
The authors are thankful to Sophisticated Analytical Instrumentation Facility (SAIF), IIT Madras, Chennai, and Nehru Memorial College, Puthanampatti, Trichirappalli, India for providing spectral measurements.
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Morokuma, N. Rega, P. Salvador, JJ. Dannenberg, D.K. Malich, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stetanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. AL-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gonzalez, M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 98, Revision A. Vol. 11.4, Gaussian Inc., Pittsburgh, PA, 2002.
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[18] G. Keresztury. Raman spectroscopy: Theory, in: J.M. Chalmers. P.R.
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[28] P.L. Peasole, L.D. Shields, T. Cairus, I.C. McWilliam. Modern Methods of
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Bond length | Value(A°) | Bond angles | Value(°) | |||
p-BBA | P-FBA | p-BBA | P-FBA | |||
C1-C2 | 1.394 | 1.394 | C1-C2-C3 | 119.994 | 119.994 | |
C2-C3 | 1.395 | 1.395 | C2-C3-C4 | 119.994 | 119.994 | |
C3-C4 | 1.394 | 1.394 | C3-C4-C5 | 120.0061 | 120.0061 | |
C4-C5 | 1.395 | 1.395 | C4-C5-C6 | 119.008 | 119.008 | |
C5-C6 | 1.394 | 1.394 | C6-C1-C7 | 119.984 | 119.984 | |
C1-C7 | 1.540 | 1.540 | C1-C2-H8 | 120.024 | 120.024 | |
C2-H8 | 1.099 | 1.099 | C2-C3-H9 | 119.993 | 119.993 | |
C3-H9 | 1.099 | 1.099 | C3-C4-Br10(F10) | 120.010 | 120.010 | |
C4-Br10(F10) | 1.910 | 1.350 | C4-C5-H11 | 119.997 | 119.997 | |
C5-H11 | 1.099 | 1.099 | C5-C6-H12 | 120.008 | 120.008 | |
C6-H12 | 1.099 | 1.099 | C1-C7-O13 | 119.996 | 119.996 | |
C7-O13 | 1.301 | 1.301 | C1-C7-O14 | 119.886 | 119.886 | |
C7-O14 | 1.301 | 1.301 | C7-O14-H15 | 109.500 | 109.500 | |
O14-H15 | 0.960 | 0.960 |
For numbering of atoms refer figure.1 (a) and figure.1 (b)
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No. Symmetry coordinatesa Description Diagonal force constantsb
p-BBA p-FBA p-BBA p-FBA
1 S1 =r1,2 υC1C2 υC1C2 6.53 6.67
2 S2 = r2,3 υC2C43 υC2C43 6.79 7.04
3 S3 =r3,4 υC3C4 υC3C4 6.58 6.87
4 S4 =r4,5 υC4C5 υC4C5 6.60 6.87
5 S5 =r5,6 υC5C6 υC5C6 6.73 6.98
6 S6 =r6,1 υC6C1 υC6C1 6.51 6.65
7 S7 =r1,7 υC1C7 υC1C7 2.88 3.03
8 S8 =r2,8 υC2H8 υC2H8 5.09 5.01
9 S9 =r3,9 υC3H9 υC3H9 5.09 5.04
10 S10 =r4,10 υC4Br10 υC4F10 3.34 5.82
11 S11 =r5,11 υC5H11 υC5H11 5.09 5.09
12 S12 =r6,12 υC6H12 υC6H12 5.11 5.11
13 S13 =r7,13 υC7O13 υC7O13 10.89 11.17
14 S14 =r7,14 υC7O14 υC7O14 5.11 5.22
15 S15 =r14,15 υO14H15 υO14H15 5.36 5.36
16 S16 =β1,2,3 +β2,3,4 -2β3,4,5+ β4,5,6+ β1,6,5-2 β6,1,2 δRing1 δRing1 1.28 1.29
17 S17 =β1,2,3 -β2,3,4 +β3,4,5-β4,5,6+ β1,6,5- β6,1,2 δRing2 δRing2 1.91 1.62
18 S18 =β12,3 -β2,3,4 +β4,5,6 -β1,6,5 δRing3 δRing3 1.11 1.24
19 S19 =β6,1,7 -β2,1,7 δC1C7 δC1C7 1.28 1.02
20 S20 =β1,2,8 -β3,2,8 δC2H8 δC2H8 0.50 0.51
21 S21 =β2,3,9 -β4,3,9 δC3H9 δC3H9 0.51 0.49
22 S22 =β3,4,10 -β5,4,10 δC4Br10 δC4F10 0.72 0.93
23 S23 =β4,5,111 -β6,5,11 δC5H11 δC5H11 0.51 0.49
24 S24 =β5,6,12 -β1,6,12 δC6H12 δC6H12 0.51 0.52
25 S25 =β1,7,13 δC7O13 δC7O13 2.53 2.32
26 S26 =β1,7,14 δC7O14 δC7O14 2.74 2.51
27 S27 =β7,14,15 δO14H15 δO14H15 0.83 0.86
28 S28 =γ 7,1,6,2 γC1C7 γC1C7 0.04 038
29 S29 =γ 8,2,1,3 γC2H8 γC2H8 0.47 0.47
30 S30 =γ 9,3,2,4 γC6H 9 γC6H 9 0.44 0.42
31 S31 =γ 10,4,3,5 γC4Br10 γC4F10 0.56 0.31
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32 | S32 =γ 11,5,4,6 | γC5H11 | γC5H11 | 0.44 | 0.41 |
33 | S33 =γ 12,6,5,1 | γC6H12 | γC6H12 | 0.44 | 0.45 |
34 | S34 =τ13,7,1,6-τ13,7,1,2 | τC7O13 | τC7O13 | 0.10 | 1.07 |
35 | S35 =τ14,7,1,2-τ14,7,1,6 | τC7O14 | τC7O14 | 0.11 | 0.01 |
36 | S36 =τ15,14,7,1 | τO14H15 | τO14H15 | 0.15 | 0.14 |
37 | S37 =τ1,2,3,4 +τ2,3,4,5 -2τ3,4,5,6+ τ,4,5,6,1 +τ5,6,1,2 - | τRing1 | τRing1 | 0.41 | 0.48 |
38 | 2τ6,1,2,3 S38 =τ1,2,3,4 -τ2,3,4,5 +τ3,4,5,6-τ,4,5,6,1 +τ5,6,1,2 -τ6,1,2,3 | τRing2 | τRing2 | 0.30 | 0.35 |
39 | S39 =-τ1,2,3,4- τ2,3,4,5+ τ4,5,6,1 -τ5,6,1,2 | τRing3 | τRing3 | 0.32 | 0.45 |
For numbering of atoms reference Fig. 1(a) and Fig. 1(b); Abbreviations: υ: stretching; δ: deformation in- plane; γ: deformation out-of-plane; τ: torsion.
adefinitions are made in terms of the standard valence coordinates: ri,j is the bond length between atoms i and j; βi,j,k is the valence angle between atoms i,j,k where j is the central atom; γ i,j,k,l is the out-of-plane angle between the i-j bond and the plane defined by the j,k,l atoms; τi,j,k,l is the torsional (dihedral) angle between the plane defined by i,j,k and j,k,l atoms.
bStretching force constants are given in mdyn Aº -1, being and torsion force constants are given in mdyn Aº.
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Sl. No | Symmetry species Cs | Observed wavenumbers cm-1 | Calculated wavenumbers B3LYP/6-31G** force field cm-1 | IR Intensity | Raman Activity | Characterization of normal modes with PED (%) | ||
FT IR | Raman | unscaled | scaled | |||||
1 | A' | 3092 | - | 3767 | 3092 | 88.770 | 175.311 | υOH(100) |
2 | A' | - | 3076 | 3233 | 3056 | 0.665 | 171.452 | υCH(99) |
3 | A' | 3068 | - | 3229 | 3053 | 1.702 | 52.305 | υCH(99) |
4 | A' | 3045 | - | 3218 | 3042 | 0.473 | 64.694 | υCH(99) |
5 | A' | 1305 | - | 3217 | 3041 | 0.045 | 20.751 | υCH(99) |
6 | A' | 1680 | - | 1820 | 1687 | 290.361 | 66.303 | υCO(64),bCO(16) |
7 | A' | - | 1611 | 1646 | 1633 | 118.660 | 166.664 | υCC (61), bCH(20),Rsymd(16) |
8 | A' | 1572 | - | 1622 | 1571 | 21.034 | 11.174 | υCC(70) |
9 | A' | 1463 | - | 1528 | 1479 | 23.692 | 2.234 | υCC (62),bCH(34), |
10 | A' | 1430 | - | 1439 | 1408 | 26.879 | 4.492 | υCC(46), bCH(36) |
11 | A' | 1354 | - | 1392 | 1357 | 15.215 | 4.351 | bCOH(51), υCO(23),bCO(12) |
12 | A' | 1325 | - | 1350 | 1316 | 7.948 | 1.694 | υCC(78),bCH(13) |
13 | A' | 1280 | - | 1328 | 1293 | 1.060 | 0.473 | bCH(65), υCC(32) |
14 | A' | 1179 | 1179 | 1218 | 1173 | 9.770 | 3.504 | bCH(69), υCC(23) |
15 | A' | - | 1134 | 1194 | 1188 | 330.914 | 90.189 | υCO(24),bCH(18),bCOH(17), υCC(16) υCCar(10) |
16 | A' | 1110 | - | 1135 | 1098 | 47.448 | 17.632 | bCH(51), υCC(31) |
17 | A' | 1079 | - | 1117 | 1072 | 97.297 | 32.978 | bCH(50), υCBr(21), υCC (16) |
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18 | A' | 1070 | 1070 | 1088 | 1056 | 80.064 | 9.172 | υCC(40), υCO(33) |
19 | A' | - | 1016 | 1028 | 1016 | 56.383 | 0.960 | Rtrigd(71), υCC(17) |
20 | A'' | 961 | - | 1003 | 966 | 0.091 | 0.117 | ωCH(92) |
21 | A'' | 928 | - | 991 | 947 | 0.040 | 1.807 | ωCH(81), ttrig(17) |
22 | A'' | 852 | - | 871 | 830 | 2.830 | 4.673 | ωCH(98) |
23 | A'' | 824 | - | 856 | 816 | 34.851 | 0.441 | ωCH(79) |
24 | A' | 818 | - | 786 | 802 | 17.986 | 17.463 | υCC (53), Rsym (18), υCBr(10) |
25 | A'' | 750 | - | 774 | 747 | 1.328 | 0.088 | ttrig(77),ωCH(10) |
26 | A' | - | 685 | 714 | 666 | 47.997 | 2.465 | bCO(48), υCO(17),bCOH (11) |
27 | A'' | - | 629 | 660 | 635 | 83.098 | 0.250 | tCO(72),tOH(13) |
28 | A' | 610 | - | 642 | 607 | 1.929 | 6.522 | Rasymd(83) |
29 | A'' | 550 | - | 605 | 550 | 44.310 | 8.675 | tOH(73) |
30 | A' | 498 | - | 508 | 511 | 8.108 | 0.346 | bCO(68),bCC(13) |
31 | A'' | 470 | - | 477 | 472 | 22.936 | 1.187 | tRasym(45), ωCBr(35) |
32 | A' | 430 | - | 461 | 437 | 11.864 | 0.689 | υCBr(41), υCC(33),bCO(10) |
33 | A'' | - | 400 | 424 | 399 | 0.005 | 0.004 | tRsym(67), ωCH(16),tRasym(13) |
34 | A' | - | 279 | 283 | 280 | 0.097 | 0.101 | bCBr(42),bCO(32),bCC(17) |
35 | A' | - | 250 | 254 | 251 | 1.339 | 2.816 | Rsym(36),υCBr(27), υCC (21) |
36 | A'' | - | 205 | 247 | 209 | 0.336 | 1.395 | ωCBr(30),tRasym(21),tCO(21),tRsym(10)) |
37 | A' | - | 150 | 155 | 157 | 0.947 | 0.397 | bCC(43),bCBr(27),bCO(23) |
38 | A'' | - | 79 | 80 | 66 | 03154 | 0.022 | ωCC(48), ωCH(14),tRasym(12) |
39 | A'' | - | 70 | 73 | 61 | 0.832 | 0.975 | tCO(99) |
Abbreviations; R, ring; b, bending; d, deformation; sym, symmetric; asy, asymmetric; ω, wagging; t, torsion; trig, trigonal; υ, stretching. Only contributions larger than 10% are given.
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Sl. No | Symmetry species Cs | Observed wavenumbers cm-1 | Calculated wavenumbers B3LYP/6-31G** force field cm-1 | IR Intensity | Raman Activity | Characterization of normal modes with PED (%) | ||
FT IR | Raman | unscaled | scaled | |||||
1. | A' | - | 3094 | 3767 | 3094 | 80.658 | 151.598 | υOH(100) |
2. | A' | 3084 | - | 3233 | 3035 | 1.350 | 141.737 | υCH(99) |
3. | A' | - | 3078 | 3229 | 3031 | 2.479 | 85.614 | υCH(99) |
4. | A' | 2997 | - | 3218 | 3021 | 1.834 | 107.581 | υCH(99) |
5. | A' | 2952 | - | 3217 | 3013 | 285.969 | 23.650 | υCH(99) |
6. | A' | 1686 | - | 1819 | 1699 | 137.127 | 39.540 | υCO(67),bCO(13) |
7. | A' | - | 1634 | 1663 | 1650 | 11.243 | 77.967 | υCC(63), bCH(18),Rsymd(13) |
8. | A' | 1629 | - | 1642 | 1614 | 50.676 | 7.697 | υCC(71) |
9. | A' | 1511 | 1511 | 1555 | 1516 | 9.729 | 3.567 | υCC(52), bCH(37) |
10. | A' | 1431 | - | 1453 | 1429 | 7.451 | 1.542 | υCC(53), bCH(34) |
11. | A' | 1366 | - | 1393 | 1371 | 4.594 | 2.492 | bCOH(59), υCO(23),bCO(10) |
12. | A' | 1332 | 1332 | 1363 | 1342 | 4.734 | 2.458 | υCC(90) |
13. | A' | 1298 | - | 1317 | 1297 | 38.000 | 1.571 | bCH(86) |
14. | A' | 1237 | - | 1286 | 1239 | 38.509 | 6.297 | υCF(50), υCC(22),bCH(15),Rtrigd(11) |
15. | A' | 1161 | - | 1211 | 1166 | 389.522 | 18.465 | bCH(52), υCC(13) |
16. | A' | - | 1153 | 1177 | 1144 | 33.565 | 52.343 | bCH(24), υCO(21), υCC(16), bCOH(12) |
17. | A' | 1108 | - | 1128 | 1102 | 107.536 | 8.771 | bCH(60), υCC(29) |
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18. | A' | 1096 | - | 1112 | 1064 | 7.801 | 2.360 | υCO(40), υCC(29) |
19. | A' | 1016 | - | 1031 | 1011 | 0.470 | 0.251 | υCC(52), Rtrigd(32), bCH(14) |
20. | A'' | 969 | - | 986 | 948 | 0.447 | 0.301 | ωCH(91) |
21. | A'' | 929 | - | 971 | 916 | 20.146 | 1.797 | ωCH(87), tRtrig(11) |
22. | A' | 856 | - | 863 | 840 | 7.662 | 24.234 | Rtrig(36),CC(29), CF(17) |
23. | A'' | - | 829 | 854 | 816 | 0.036 | 0.167 | ωCH(43),tRtrig(32), ωCC(14) |
24. | A'' | 770 | - | 835 | 812 | 20.093 | 5.178 | ωCH(97) |
25. | A'' | 761 | - | 771 | 761 | 85.827 | 0.451 | tRtrig(56),ωCH(33) |
26. | A'' | 723 | - | 730 | 726 | 15.688 | 0.366 | tCO(57),ωCH(35) |
27. | A' | 665 | - | 699 | 580 | 0.447 | 2.991 | υCC (29), bCO(21), υCO(15),Rtrigd(11) |
28. | A' | - | 637 | 645 | 641 | 1.002 | 7.276 | Rasymd(79), υCC(10), |
29. | A' | 600 | - | 603 | 583 | 56.482 | 0.865 | bCO(37), Rsymd(27), υCF(12) |
30. | A'' | 550 | - | 593 | 551 | 54.995 | 6.316 | tOH(52),tRsym(28) |
31. | A' | 497 | - | 508 | 495 | 5.437 | 0.480 | bCO(64),bCC(13) |
32. | A'' | 490 | - | 504 | 487 | 32.698 | 3.119 | tRasym(58), tOH(16), ωCH(14) |
33. | A'' | - | 426 | 426 | 428 | 0.885 | 0.111 | tRsym(74), ωCH(12) |
34. | A' | - | 386 | 399 | 390 | 5.717 | 0.294 | bCF(54),bCO(28) |
35. | A' | - | 315 | 347 | 323 | 0.881 | 2.309 | Rsymd(48), υCC (28) |
36. | A'' | - | 245 | 299 | 245 | 2.252 | 2.479 | ωCF(61), ωCC(31) |
37. | A' | - | 190 | 194 | 193 | 1.469 | 0.170 | bCC(46),bCO(45) |
38. | A'' | - | 98 | 111 | 104 | 0.192 | 0.001 | ωCC(47), ωCF(18), ωCH(14) |
39. | A'' | - | 70 | 73 | 71 | 0.818 | 1.084 | tCO(99) |
Abbreviations; R, ring; b, bending; d, deformation; sym, symmetric; asy, asymmetric; ω, wagging; t, torsion; trig, trigonal; υ, stretching. Only contributions larger than 10% are given.
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(a)
(b)
Wavenumber (cm-1)
(a) calculated with B3 LYP/6-31G**
(b) observed with KBr disc
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(a)
(b)
Wavenumber (cm-1)
Fig. 3 Comparison of observed and calculated FT-Raman spectra of p- bromo benzoic acid
(a) calculated with B3 LYP/6-31G**
(b) observed with KBr disc
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(a)
(b)
Wavenumber (cm-1)
Fig.4 Comparison of observed and calculated FTIR spectra of p- fluoro benzoic acid
(a) calculated with B3 LYP/6-31G**
(b) observed with KBr disc
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(a)
(b)
Wavenumber (cm-1)
Fig.5 | Comparison of observed and calculated | FT-Raman Spectra |
of p- fluoro benzoic acid (a) Calculated with B3 LYP/6-31G** (b) Observed with KBr disc |
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