Benzoic Acid - Spectroscopy

Asian Journal of Spectroscopy, 11,3&4, 2007, 169-172 Spectroscopic and Intra Molecular Studies of Pharmaceutically Important Benzoic Acid and its Amino Substitutents Y.P.Singha, R.A.Singhb and Ratnesh Dasc a

Department of Physics, Govt. Women’s Polytechnic College, Sagar (MP), INDIA 470001.E-mail: [email protected] b Department of Physics, Dr. H.S.Gour University, Sagar (MP), INDIA, 470001 c Department of Chemistry, Dr. H.S.Gour University, Sagar (MP), INDIA, 470001, E-mail: [email protected] ABSTRACT The vibrational absorption spectra of Benzoic Acid’s Monomer molecules and its amino substitutents have been studied using GF matrix and AM1 method. Assuming C s point symmetry, vibrational assignments for the observed frequencies have been proposed. The spectra exhibit distinct features originating from low frequency vibrational modes caused by intra-molecular motion. Normal modes have been calculated and an assignment of the observed spectra has been proposed. Experimental frequencies are compared with those obtained by G.F.Matrix and AM1 method. Keywords : Benzoic Acid,o-, m-, p- Amino Benzoic Acid, FTIR Spectra, AM1, G.F.Matrix INTRODUCTION Carboxylic

acids (RCOOH) are a common and important functional group and provide

the point of success to the carboxylic acids derivatives (acetyl chlorides, esters, amides etc.) and therefore, it has been extensively studied by spectroscopic methods. Spectroscopist's interest has been concerned with structure and vibrational frequencies. The aim of the present study is a IR spectroscopic analysis of Benzoic Acid (BA), which have found considerable attention in the literature1-8. We compared experimental results with calculated frequencies of BA using force matrix method and AM1, PM3 and G.F. Matrix method. These methods were able to account breadth of spectrum as well as description of vibrational modes to encourage the application of a similar procedure to a larger and more complex group.

STRUCTURE AND GEOMETRY OF BENZOIC ACID Benzene derivatives containing a carboxylic or amino group possess C 1 symmetry. From aniline and toluene, the geometry parameters were transferred. Cartesian coordinates of the molecules under investigation were calculated on the basis of geometrical parameters as shown in Table 1 EXPERIMENTAL Benzoic acid was purchased from Sigma Chemical Co (USA). Benzoic acid forms a white to off white crystalline powder with melting point of 159 c. I.R.

Spectrum

has

been

recorded in the liquid phase in the range 400-4000cm-1 on Perkin-Elmer spectrometer Model 397. Preparation of KBr Pallets: A small amount of finally grounded solid sample was intimately mixed with about 100 times or more than its weight of Potassium bromide powder. The finally grounded mixture was than pressed under very high pressure in a press (about 10/cm2) to form a small pallet (about 1-2 mm thick and 1cm in diameter). The accuracy of the measurements was estimated to be within 3cm-1 and the resolution was better than 2cm-1 through the entire range for both the spectra. COMPUTATIONAL AND THEORETICAL DETAILS In noncomplex molecules, the G F Matrix 9 is given by:G tt’= Σ3Ni=1 (B ti B t’i’) 1/ mi

where t, t’ = 1,2,3,……, 3N-6

In which mi is the mass of the atom to which the subscript I refers and Bti , Bt’i’ are constants determined by geometry of molecule. Internal coordinate St are related with Cartesian displacement coordinate ξi as : St = Σ 3Ni=1 Bti ξi

where t = 1,2,3….., 3N-6

On solving G.F. matrix for any atom α is obtained as: G tt’= Σ3N α =1 μ α St α . St’ α Where dot represents the scalar product of two vectors and μ α = 1/m α , the reciprocal of the mass of atom α The AM1 program

10

semi empirical approaches was performed as implemented in MOPAC

and the PRECISE keywords were used. We have transformed the harmonic force

fields, determined initially in the Cartesian coordinates, were transformed to the force fields in

the internal local coordinates. The force fields obtained were used to calculate the potential energy distribution (PED)11. Contributions greater than 10% are given. RESULTS and DISCUSSIONS We had employed a very large basis set for the computational of the frequencies. First infrared frequencies were calculated for the BA ( Cs Symmetry) at the AM1 and G F Matrix level of theory. We can get information from computational vibrational spectra only when we compare it with experimental spectrum.Our results are given in table 2. Due to anharmonicity, the harmonic vibrational frequencies were found to be lowered by1 to 3% in GF Matrix method except AM1 method. Benzoic acid contains 15 atoms so that it has 39 normal modes. The calculated normal modes are distributed among 27 a΄ and 12 a΄΄ species of Cs symmetry group. The table 2 also shows that PED contributions for 39 normal modes. These assignments are partly based on the calculated frequencies. As the table 2 is self-explanatory, we shall discuss here only some important points. OH Stretch: Experimental OH stretch band frequency for BA is 3507 cm −1 which was shifted by 97 cm −1 as reported by Antony et al13 and which is also higher than those observed by others7,16. Theoretically calculated frequencies by G.F. and AM1 are 3579.2 cm −1 and 3627.6 cm −1

, respectively.

CH3 s-stretch: As presented in table2, experimental CH3 s-stretch frequency for BA is 2987 cm −1

. Antony et al13 observed this frequency for benzoic acid at 2943 cm −1 . Calculated frequencies

by G.F. and AM1 are 3010.9 cm −1 and 3172.0 cm −1 respectively. C=O stretch: experimental observed frequencies for this bands is 1823 cm −1 for BA, which is higher than the calculated frequencies . Antony et al13 observed this frequency for benzoic acid at 1752 cm −1 . Theoretically calculated frequencies by G.F. and AM1 are 1716.5 cm −1 and 1726.2 cm −1 respectively. O-H Bend: Our observations for this bend is 1328BA. Antony et al13 observed this frequency for benzoic acid at 1381 cm −1 . Trout et al observed 1328 frequency for COO symmetric stretch, so our assignment was totally reversed by this one. Computationally calculated frequencies by G.F. and AM1 are 1311.5 cm −1 and 1441.9 cm −1 respectively.

C-O stretch: Experimental frequency for BA is 1228 cm −1 respectively. Antony et al13 did not observed this frequency for benzoic acid. Theoretically calculated frequencies by G.F. and AM1 are 1243.8 cm −1 and 1435.7 cm −1 respectively. O-C-O Deformation: We observed this bend frequency at 668 cm −1 for BA respectively which is comparative to others14,16 . Theoretically calculated frequencies by G.F. and AM1 are 657.7 cm −1 and 646.3 cm −1 respectively. Torsion: Experimental observed frequency for this bend for BA is 591 cm −1 . Antony et al15 observed this frequency for benzoic acid at 444 cm −1 . Computationally calculated frequencies by G.F. and AM1 are 593.4 cm −1 and 571.9 cm −1 respectively. NH 2 Group Modes The number of internal vibrations for a group is given by 3m-3, where m is the number of atoms in the group. Thus NH 2 has 6 modes of vibrations. These modes are as : two stretching vibrations ( one symmetric and one asymmetric) both belonging to a’ species, two angle deformations (scissoring and rocking), one out-of-plane wagging of NH 2 and one torsion vibration of NH 2 . There are three major differences between the C-H and N-H stretching frequencies. First, the force constant for N-H stretching is stronger, there is a larger dipole moment associated with the N-H bond, and finally, the N-H bond is usually involved in hydrogen bonding. The stronger force constant leads to a higher frequency for absorption. The N-H stretching frequency is usually observed from 3500-3200 cm-1. The larger dipole moment leads to a stronger absorption and the presence of hydrogen bonding has a definite influence on the band shape and frequency position. The NH 2 stretching modes appear in the region 3500 – 3100 cm −1 and the asymmetric component has slightly higher magnitude than the symmetric

component.

D.N.Singh

19

observed asymmetric modes at 3465 cm −1 and symmetric mode at 3360 cm −1 . However, A.K.Tiwari 20 observed them at 3449 cm −1 and 3367 cm −1 respectively.

He observed in-plane bending and rocking mode at 1630 cm −1 and 1055 cm −1 respectively. A.K.Tiwari19 got in-plane bending mode at 1621 cm −1 and rocking mode at 952 cm −1 . D.N.Singh 20 observed wagging vibration at 592 cm −1 and he didn’t got torsion mode. A.K.Tiwari19 observed these vibrations at 626 cm −1 and 274 cm −1 respectively. In present study we get frequencies for them as shown in table 3. COOH Group Modes In the parent molecule benzene if one of the hydrogen atom is replaced by a COOH group, nine more normal modes would appear. They are as:- O-H Stretching, C-O Stretching, C=O Stretching, in-plane-rocking, in-plane bending of C-O, in-plane-bending of C=O, inplane-bending of OH, out-of-plane wagging, and

out-of-plane torsion.. J. Antony et al13

studied vibrational spectra of benzoic acid and got C=O Stretching at 1745 cm −1 , C-O stretching at 1050 cm −1 , C-O in-plane bending at 594 cm −1 , C=O in-plane bending at 1804 cm −1 , OH stretch at 3785 cm −1 , rocking mode at 554 cm −1 , torsion mode at 594 cm −1 and wagging mode at 441 cm −1 . Florio et aI

15

observed C=O Stretching at 1752 cm −1 , C-O

stretching at 1347 cm −1 , C-O in-plane bending at 628 cm −1 , OH stretch at 3785 cm −1 , rocking mode at 628 cm −1 ,

and wagging mode at 160 cm −1 . In present study we get

frequencies as shown in table 4. CONCLUSIONS Theoretical semi-empirical quantum mechanical AM1 and GF matrix calculations of the geometry and vibrational frequencies of the Benzoic acid and its amino substitutents

are

presented in this paper and compared with infrared spectra. The calculated geometries and frequencies agree well with the experimental ones, but there are some differences between frequencies mainly due to intermolecular interactions, anharmonicity and computational basis set. ACKNOWLEDGEMENTS The authors are grateful to Director, Directorate of Technical Education-Madhya Pradesh, Bhopal and Head, Department of Physics, Dr. H.S.Gour University, Sagar (MP), India and

Central Drug Research Institute, Lucknow, India for IR spectra, Hypercube Inc for providing Hyperchem Package 7 for molecular modeling.

Table 1 Assumed Bond Length and Bond angle in Benzoic and Amino Benzoic Acids. Bond Angle ( Degree )

Bond

Bond length ( A 0 ) By DFT Experime Method 18 ntal

By MOPAC Calculation

Bond Angle

By DFT Method 18

O2 – H6

1.00

0.98

1.06

C7 O2 H6

110.27

C 7 – O1

1.230

1.26

1.19

O1 C 7 O 2

123.26

122.2

122.81

C7 – O2

1.323

1.27

1.21

O 2 C 7 C1

114.50

118.0

118.10

C 7 – C1

1.486

1.48

1.10

C1 C 7 O1

122.24

122.0

121.42

C1 – C 2

1.400

1.39

1.40

C 7 C1 C 2

121.40

118.0

121.53

C2 – C3

1.391

1.38

1.39

C 6 C1 C 7

119.90

119.9

119.96

C3 – C 4

1.395

1.37

1.40

C 6 C1 C 7

118.70

118.8

119.96

C 4 – C5

1.395

1.38

1.39

C1 C 2 C 3

119.86

120.1

120.00

C5 – C6

1.390

1.40

1.40

C2 C3C 4

120.02

119.9

119.98

C 6 – C1

1.400

1.39

1.39

C3C 4 C5

120.15

120.3

120.02

C 2 – H1

1.082

0.79

1.10

119.98

119.7

119.98

C3 – H2

1.084

0.96

1.10

C 4 C5C6 C5C6C7

120.02

119.8

119.99

C4 – H3

1.084

0.91

1.10

C1 C 2 H1

119.48

119

120.00

C5 – H 4

1.084

0.96

1.10

H1 C 2 C 3

120.66

121

120.00

1.083

0.79

1.10

C2 C3H2

119.85

120

119.99

1.103

1.10

1.11

120.07

119

120.00

1.154

1.12

1.13

H2 C3C 4

119.91

118

119.50

119.94

118

119.63

C6 – H5 C–N N-H

C3C 4 H3 H3C 4 C5

Experime ntal

By MOPAC Calculation 106.00

120.09

119

120.01

C3C5H 4

119.93

120

119.96

H 4 C5C6

121.12

121

121.23

C5C6H5

118.86

118

118.63

H 5 C 6 C1 CNH HNH

119.98

119

119.99

148.95

150

147.95

103

95.6

Table 2 Experimental and Calculated Frequencies and Potential Distribution in C 6 H 5 COOH Assignme G F Matrix Frequencies nt Experimental (in cm −1 ) Frequencies Frequencies PED and Mode AM1 −1 −1 (in cm ) (in cm ) 1 2 3 4 5 6 7 8

3507 3217 3130 3100 3087 2987 1823 1696

3579.2 3210.6 3118.8 3111.5 3072.4 3010.9 1716.5 1648.1

9 10

1585 1499

1561.4 1518.7

11 12 13 14 15 16 17 18 19

1456 1328 1228 1292 1280 1186 1179 1129 1074

1443.8 1311.5 1243.8 1312.3 1277.3 1171.4 1192.5 1134.6 1063.1

20 21 22 23 24

1029 1000 808 668 600

1011.1 1013.9 801.3 652.7 587.3

25 26 27

548 420 317

525.6 412.1 310.5

OH str CH str CH str CH str CH str CH str C=O str CC ring deformation C-C str COH bnding

3627.3 3188.2 3190.2 3102.2 3175.7 3172.0 1786.2 1921

CCH bending OH bending C-O str CCh bending O-H bend CH ib COH bending Ring id+C-O str Ring CCH bending Ring id + CC str CH od CH od OCO deform Ring CCC bending COH bending C-O bending C=O bending

1572.6 1441.9 1435.7 1378.9 1359.0 1314.7 1229.4 1198.3 1177.5

1765.5 1638.6

1168.0 1089.4 796.5 646.3 536.8 509.9 409.6 286.0

Assig nment

Experiment al Frequencies (in cm −1 )

28 29 30 31 32 33 34 35 36 37 38 39

980 970 935 850 812 709 664 613 591 190

G F Matrix Frequenci es (in cm −1 ) 971.6 967.3 929.5 937.6 844.1 801.9 719.8 657.1 609.3 593.4 199.4 57.6

PED and Mode

CC wagging CC wagging rocking CC wagging Ring CCH Ring CCH bend C=O o.p.bend Ring CCH bend torsion torsion wagging twisting

Frequencies (in cm −1 ) AM1

1013.2 995.6 971.8 894.5 886.3 825.9 723.6 610.2 611.9 571.92 150.6 44.0

Table 3 Internal Vibrations of NH 2 group Mode of Vibration

a’

a”

N-H Asymmetric Stretching CN-H Symmetric Stretching NH 2 In-Plane Bending NH 2 Rocking Wagging Torsion

o-Amino Benzoic Acid (in cm −1 ) 3622 (E), 3601.6(GF) 3530.9(M) 3325(E), 3342.9(GF) 3530.9(M) 1156(E), 1162.3(GF) 1219.5(M) 536(E), 527.1(GF) 558.1(M)

m-Amino Benzoic Acid (in cm −1 ) 3472(E), 3490.1(GF) 3492.4(M) 3225(E), 3207.6(GF) 3464.6(M) 1110(E), 1123.5(GF) 1217.7(M) 541(E), 531.3(GF) 537.2(M)

p-Amino Benzoic Acid (in cm −1 ) 3509(E), 3521.3(GF) 3512.2(M) 3462(E), 3487.2(GF) 3490.0(M) 1132(E), 1140.1(GF) 1143.9(M) 523(E), 529.3(GF) 539.3(M)

459(E), 441.8(GF) 440.5(M) 279(E), 284.7(GF) 281.7(M)

432(E), 441.8(GF) 497.4(M) 281(E), 280.2(GF) 251.2(M)

412(E), 408.3(GF) 380.2(M) 291(E), 300.1(GF) 326.0(M)

E :- Experimental frequencies GF:- Theoretical frequencies calculated by GF Matrix method M:- Theoretical frequencies calculated by MOPAC method

Table 4 Internal Vibrations of COOH group Mode of Vibration O-H Stretching a’ C-O Stretching C=O Stretching Bending C-O Bending C=O Bending OH

Rocking a” Wagging Torsion

Benzoic Acid (cm −1 ) 3389 (E) 3379.2(GF) 3427.3(M) 1823(E) 1818.1(GF) 1821.0(M) 1696(E) 1716.5(GF) 2076.2(M) 420(E) 412.1(GF) 409.6(M) 317(E) 310.5(GF) 200.0(M) 1328(E) 1343.8(GF) 1435.7(M)

o-Amino Benzoic Acid (cm −1 ) 3338(E) 3315.6(GF) 3427.8(M) 1856(E) 1846.3(GF) 1959.2(M) 1590(E) 1581.5(GF) 1549.9(M) 440(E) 421.5(GF) 414.5(M) 351(E) 362.4(GF) 259.5(M) 1360(E) 1358.9(GF) 1355.5(M)

m-Amino Benzoic Acid (cm −1 ) 3420(E) 3431.1(GF) 3427.5(M) 1845(E) 1863.2(GF) 2075.5(M) 1603(E) 1621.1(GF) 1551.2(M) 450(E) 431.3(GF) 437.2(M) 335(E) 338.2(GF) 334.3(M) 1310(E) 1321.6(GF) 1435.5(M)

p-Amino Benzoic Acid (cm −1 ) 3400(E) 3429.1(GF) 3431.7(M) 1793(E) 1728.2(GF) 1737.3(M) 1657(E) 1631.1(GF) 1600.7(M) 441(E) 411.2(GF) 416.4(M) 366(E) 371.1(GF) 377.5(M) 1337(E) 1332.3(GF) 1331.7(M)

664(E) 657.1(GF) 610.2(M) 288(E) 293.4(GF) 271.9(M) 709(E) 719.8(GF) 723.6(M)

601(E) 619.3(GF) 637.1(M) 293(E) 284.7(GF) 281.7(M) 758(E) 751.8(GF) 753.5(M)

650(E) 579.4(GF) 579.5(M) 293(E) 285.2(GF) 266.7(M) 789(E) 751.7(GF) 744.1(M)

692(E) 706.2(GF) 754.3(M) 291(E) 300.1(GF) 326.0(M) 768(E) 786.1(GF) 875.3(M)

E :- Experimental frequencies GF:- Theoretical frequencies calculated by GF Matrix method M:- Theoretical frequencies calculated by MOPAC method

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