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VIBRATIONAL ANALYSIS OF P-BROMO BENZOIC ACID AND P-FLUORO BENZOIC ACID AND SIMULATION OF FTIR AND FT-RAMAN SPECTRA BASED ON

SCALED QUANTUM FORCE FIELDS

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

_______________________________________________________________________________________________

Abstract

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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1. Introduction

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.

2. Experimental

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.

3. Computational Details

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.

3.1. Prediction of Raman intensities

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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4. Results and Discussion

4.1. Molecular geometry

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.

4.2. Vibrational force constants

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.

4.3. Vibrational spectra

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.

4.3.1. C-H vibrations

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.

4.3.2. Carboxylic Acid

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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4.3.3. C-Br vibrations

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].

4.3.4. C-F vibrations

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.

4.3.5. Ring vibrations

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].

5. Conclusion

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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Table1

Optimized geometrical parameters of p-bromo benzoic acid (p-BBA) and p-fluoro benzoic acid


(p-FBA) obtained by B3LYP6-31G** density functional calculations.

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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Table 2

Definition of local symmetry coordinates and diagonal force constants of p-bromo benzoic acid and p-fluoro benzoic acid

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 1,2,3 2,3,4 -2β3,4,5+ β4,5,6+ β1,6,5-2 β6,1,2 δRing1 δRing1 1.28 1.29

17 S17 1,2,3 2,3,4 3,4,5-β4,5,6+ β1,6,5- β6,1,2 δRing2 δRing2 1.91 1.62

18 S18 12,3 2,3,4 4,5,6 1,6,5 δRing3 δRing3 1.11 1.24

19 S19 6,1,7 2,1,7 δC1C7 δC1C7 1.28 1.02

20 S20 1,2,8 3,2,8 δC2H8 δC2H8 0.50 0.51

21 S21 2,3,9 4,3,9 δC3H9 δC3H9 0.51 0.49

22 S22 3,4,10 5,4,10 δC4Br10 δC4F10 0.72 0.93

23 S23 4,5,111 6,5,11 δC5H11 δC5H11 0.51 0.49

24 S24 5,6,12 1,6,12 δC6H12 δC6H12 0.51 0.52

25 S25 1,7,13 δC7O13 δC7O13 2.53 2.32

26 S26 1,7,14 δC7O14 δC7O14 2.74 2.51

27 S27 7,14,15 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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ISSN 2229-5518

Table 3

Detailed assignment of fundamental vibrations of p-bromo benzoic acid by normal mode analysis based on SQM force field calculations


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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Table 4

Detailed assignment of fundamental vibrations of p-fluoro benzoic acid by normal mode analysis based on SQM force field calculations

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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International Journal of Scientific & Engineering Research, Volume 5, Issue 4, April-2014 1555

ISSN 2229-5518


(a) (b)

Fig.1 Molecular model of (a) p-bromo benzoic acid and (b) p-fluoro benzoic acid along with numbering of atoms.

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(a)

(b)


Wavenumber (cm-1)

Fig.2 Comparison of observed and calculated FTIR spectra of p- bromo benzoic acid

(a) calculated with B3 LYP/6-31G**
(b) observed with KBr disc

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International Journal of Scientific & Engineering Research, Volume 5, Issue 4, April-2014 1557

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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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ISSN 2229-5518

(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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International Journal of Scientific & Engineering Research, Volume 5, Issue 4, April-2014 1559

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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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