Molecular structure and vibrational investigation of benzenesulfonic acid methyl ester using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) theory calculations

Spectrochimica Acta Part A 78 (2011) 168–178

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Molecular structure and vibrational investigation of benzenesulfonic acid methyl ester using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) theory calculations P. David Suresh Babu a,∗ , S. Periandy b , S. Mohan c , S. Ramalingam d , B.G. Jayaprakash e a

Wyckoff Junior College, Muttathur, Villupuram, Tamilnadu, India Department of Physics, Tagore Arts College, Puduchery, India Department of Mathematical and Physical Sciences, Hawassa University, Hawassa, Ethiopia d Department of Physics, A.V.C. College, Mayiladuthurai, Tamilnadu, India e Department of Physics, Sastra University, Thanjavur, India b c

a r t i c l e

i n f o

Article history: Received 12 July 2010 Received in revised form 4 August 2010 Accepted 8 September 2010 Keywords: Benzenesulfonic acid methyl ester LSDA B3LYP B3PW91 IR intensities Raman activities Spectrograms and methyl substitutions

a b s t r a c t The FT-Raman and FT-IR spectra for benzenesulfonic acid methyl ester (BSAME) have been recorded in the region 4000–100 cm−1 and compared with the harmonic vibrational frequencies calculated using DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) method by employing 6-311G (d, p) basis set with appropriate scale factors. IR intensities and Raman activities are also calculated by DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) methods. Optimized geometries of the molecule have been interpreted and compared with the reported experimental values for sulfonic acid and some substituted sulfonic acids. The experimental geometrical parameters show satisfactory agreement with the theoretical prediction from DFT. The scaled vibrational frequencies at LSDA/B3LYP/6-311G (d, p) seem to coincide with the experimentally observed values with acceptable deviations. The theoretical spectrograms (IR and Raman) have been constructed and compared with the experimental FT-IR and FT-Raman spectra. Some of the vibrational frequencies of the sulfonic acid are effected upon profusely with the methyl substitution in comparison to benzene sulfonamide and these differences are interpreted. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Benzenesulfonic acid is a very strong acid and with aromatic components are interesting chemical reagents [1]. Their functionality in catalytic materials such as sulfonated polystyrene resins is not yet fully understood [2]. It is derived directly from their acidity, including possible cooperative effects between acid groups and hydration of the resin matrix. Benzenesulfonic acid is also used as an acidic catalyst in esterification and dehydration reactions and its groups can be bound to the surface of inert support materials to form solid acid catalysts [3]. The acidic and catalytic properties of sulfonic acids support on polystyrene, silica (via propyl and phenyl tethers) and on a fluorinated hydrocarbon polymer. Polystyrene supported sulfonic acids are widely applied industrially [4–9] in bisphenol syntheses. Benzenesulfonic acid with methyl esters are widespread in nature and are widely used in industry. In nature, fats are generally triesters derived from glycerol and fatty acids. Methyl esters are responsible for the aroma of many fruits, including apples, pears, bananas, pineapples, and strawberries [10]. Several billion kilograms of polyesters are produced annually in industries, of which polyethylene

∗ Corresponding author. Tel.: +91 9443800764; fax: +91 9443800764. E-mail address: [email protected] (P.D.S. Babu). 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2010.09.017

terephthalate, acrylate esters, and cellulose acetate are important products [11]. Sulfonic acids such as sulfonic acid methyl ester and benzenesulfonic acid are often used during manufacture of pharmaceuticals [12]. Varieties of pharmaceutical drugs are prepared as salts of benzenesulfonic acid and are known as besylates or besilates. The alkali metal salt of benzenesulfonic acid is used in the production of phenol and resorcinol. Because of its wide applications, the surface enhanced FT-IR and FT-Raman studies, vibrational spectra of benzenesulfonic acid and methyl ester derivatives have been extensively investigated. Sierra Rayne and Kaya Forest have extensively studied the thermodynamic properties of perfluoroalkyl sulfonic acids [13]. More recently, Mehmet Karabacak et al. [14] have studied the structural properties of para-halogen benzenesulfonamides together with the vibrational assignments. However, a detailed DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) at 6-311G (d, p) comparative study on the complete FT-IR and FT-Raman spectra of BSAME has not been reported so far. In the present study, molecular geometry, optimized parameters and vibrational frequencies are computed and the performance of the computational methods for hybrid density functional methods (LSDA, B3LYP, B3PW91 and MPW1PW91) at 6-311G (d, p) basis sets are compared. These methods predict relatively accurate molecular structure and vibrational spectra with moderate computational effort.

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the Lee–Yang–Parr correlation function (B3LYP) [19,20], Becke’s three parameter exact exchange-function (B3) [20] combined with gradient-corrected correlational functional of Lee, Yang and Parr (LYP) [21,22] and Perdew and Wang (PW91) [23,24] and the Barone and Adamo’s Becke-style one-parameter functional using the modified Perdew–Wang exchange and Perdew–Wang 91 correlation method (mPW1PW91) predict the best results for molecular geometry and vibrational wave numbers for moderately larger molecule [25–28]. 2. Experimental details The compound under investigation namely BSAME is purchased from Sigma–Aldrich Chemicals, USA which is of spectroscopic grade and hence used for recording the spectra as such without any further purification. The FT-IR spectra of the compounds are recorded in Bruker IFS 66 V spectrometer in the range of 4000–100 cm−1 . The spectral resolution is ±2 cm−1 . The FT-Raman spectra of these compounds are also recorded in the same instrument with FRA 106 Raman module equipped with Nd:YAG laser source operating at 1.064 ␮m line widths with 200 mW power. The spectra are recorded in the range of 4000–100 cm−1 with scanning speed of 30 cm−1 min−1 of spectral width 2 cm−1 . The frequencies of all sharp bands are accurate to ±1 cm−1 . 3. Computational methods

Fig. 1. Molecular structure of benzenesulfonic acid methyl ester.

In particular, for polyatomic molecules the DFT methods lead to the prediction of more accurate molecular structure and vibrational frequencies. In DFT methods, local-spin density approximation LSDA [15–18] generally gives good molecular structures, vibrational frequencies and charge densities in strongly bounded systems, Becke’s three parameter hybrids function combined with

The molecular structure of the BSAME in the ground state is computed by performing DFT (LSDA, B3LYP, B3PW91 and MPW1PW91) with 6-311G (d, p) basis sets. The optimized structural parameters are used in the vibrational frequency calculations in DFT method. The minimum energy of geometrical structure is obtained by using level 6-311G (d, p) basis sets. The calculated frequencies are scaled by 0.913, 0.906, 0.990, 1.03and 1.15 for LSDA/6-311G (d, p) [29,30], B3LYP/6-311G (d, p) basis set is scaled with 0.920, 0.975, 0.935, 0.963, 1.01 and 1.06, B3PW91/6-311G (d, p) basis set is scaled with 0.911, 0.970, 0.980, 0.933 and 1.06 and MPW1PW91/6-311G (d, p) basis set is scaled with 0.910, 0.933, 0.977, 0.949 and 1.06. The theoretical results have enabled us to make the detailed assignments of the experimental IR and Raman

Fig. 2. Comparative graph of bond length between differences levels of DFT.

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Table 1 Optimized geometrical parameters for benzenesulfonic acid methyl ester computed at LSDA/6-311G (d, p), B3LYP/6-311G (d, p), B3PW91/ 6-311G (d, p) and MPW1PW91/6311G (d, p) basis sets. Geometrical parameters

Methods LSDA/6-311G (d, p)

˚ Bond length (A) C1–C2 C1–C6 C1–S12 C2–C3 C2–H7 C3–C4 C3–H8 C4–C5 C4–H9 C5–C6 C5–H10 C6–H11 S12–O13 S12–O14 S12–O15 O15–C16 C16–H17 C16–H18 C16–H19 Bond angle (◦ ) C2–C1–C6 C2–C1–S12 C6–C1–S12 C1–C2–C3 C1–C2–H7 C3–C2–H7 C2–C3–C4 C2–C3–H8 C4–C3–H8 C3–C4–C5 C3–C4–H9 C5–C4–H9 C4–C5–C6 C4–C5–H10 C6–C5–H10 C1–C6–C5 C1–C6–H11 C5–C6–H11 C1–S12–O13 C1–S12–O14 C1–S12–O15 O13–S12–O14 O13–S12–O15 O14–S12–O15 S12–O15–C16 O15–C16–H17 O15–C16–H18 O15–C16–H19 H17–C16–H18 H17–C16–H19 H18–C16–H19 Dihedral angle (◦ ) C6–C1–C2–C3 C6–C1–C2–H7 S12–C1–C2–C3 S12–C1–C2–H7 C2–C1–C6–C5 C2–C1–C6–H11 S12–C1–C6–C5 S12–C1–C6–H11 C2–C1–S12–O13 C2–C1–S12–O14 C2–C1–S12–O15 C6–C1–S12–O13 C6–C1–S12–O14 C6–C1–S12–O15 C1–C2–C3–C4 C1–C2–C3–H8 H7–C2–C3–C4 H7–C2–C3–H8 C2–C3–C4–C5

1.384 1.387 1.760 1.385 1.091 1.385 1.092 1.387 1.093 1.382 1.092 1.093 1.454 1.454 1.631 1.425 1.096 1.102 1.102 122.09 122.31 115.58 118.44 119.50 122.04 120.33 119.49 120.17 120.30 119.87 119.82 120.16 120.21 119.61 118.64 120.34 121.01 110.17 110.17 97.87 119.07 108.71 108.71 112.36 105.84 110.32 110.32 110.01 110.01 110.22 0.0 180.0 180.0 0.0 0.0 180.0 180.0 0.0 113.32 −113.32 0.0 −66.67 66.67 180.0 0.0 180.0 180.0 0.0 0.0

B3LYP/6-311G (d, p) 1.392 1.395 1.792 1.393 1.080 1.392 1.083 1.394 1.083 1.390 1.083 1.083 1.456 1.456 1.638 1.448 1.087 1.091 1.091 121.61 122.79 115.59 118.69 120.19 121.11 120.40 119.4 120.19 120.15 119.94 119.90 120.18 120.26 119.55 118.94 120.56 120.48 109.92 109.92 98.380 118.90 108.87 108.87 115.10 105.01 110.15 110.15 110.31 110.31 110.73 0.0 180.0 180.0 0.0 0.0 180.0 180.0 0.0 113.64 −113.64 0.0 −66.35 66.35 180.0 0.0 180.0 180.0 0.0 0.0

B3PW91/6-311G (d, p) 1.390 1.393 1.781 1.391 1.081 1.390 1.084 1.392 1.084 1.388 1.084 1.084 1.451 1.451 1.628 1.440 1.088 1.091 1.091 121.62 122.91 115.46 118.69 120.14 121.16 120.40 119.40 120.19 120.16 119.93 119.90 120.17 120.26 119.55 118.94 120.52 120.53 109.89 109.89 98.37 118.90 108.90 108.90 114.78 105.16 110.23 110.23 110.20 110.20 110.66 0.0 180.0 180.0 0.0 0.0 180.0 180.0 0.0 113.67 −113.67 0.0 −66.32 66.32 180.0 0.0 180.0 180.0 0.0 0.0

MPW1PW91/6-311G (d, p) 1.388 1.391 1.775 1.389 1.080 1.388 1.083 1.390 1.083 1.386 1.082 1.082 1.446 1.446 1.619 1.437 1.086 1.090 1.090 121.63 122.87 115.48 118.68 120.11 121.19 120.38 119.43 120.18 120.19 119.91 119.88 120.15 120.26 119.58 118.93 120.48 120.58 109.91 109.91 98.453 118.83 108.88 108.88 114.77 105.25 110.16 110.16 110.23 110.23 110.66 0.0 180.0 180.0 0.0 0.0 180.0 180.0 0.0 113.6 −113.6 0.0 −66.30 66.30 180.0 0.0 180.0 180.0 0.0 0.0

Experimental valuea,b,c 1.382 1.381 1.767 1.377 1.080 1.375 1.080 1.371 1.080 1.378 1.080 1.080 1.430 1.430 1.560 1.346 1.090 1.090 1.090 121.1 120.9 118.1 119.2 120.4 120.4 119.1 120.5 120.5 121.8 118.6 119.6 119.4 120.3 120.3 1195 120.3 120.3 106.7 107.9 119.5

– – – – – – – – – – – – – – – – – – –

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Table 1 (Continued) Geometrical parameters

Methods LSDA/6-311G (d, p)

C2–C3–C4–H9 H8–C3–C4–C5 H8–C3–C4–H9 C3–C4–C5–C6 C3–C4–C5–H10 H9–C4–C5–C6 H9–C4–C5–H10 C4–C5–C6–C1 C4–C5–C6–H11 H10–C5–C6–C1 H10–C5–C6–H11 C1–S12–O15–C16 O13–S12–O15–C16 O14–S12–O15–C16 S12–O15–C16–H17 S12–O15–C16–H18 S12–O15–C16–H19 a,b,c

180.0 180.0 0.0 0.0 180.0 180.0 0.0 0.0 180.0 180.0 0.0 180.0 65.51 −65.51 180.0 −61.01 61.01

B3LYP/6-311G (d, p) 180.0 180.0 0.0 0.0 180.0 180.0 0.0 0.0 180.0 180.0 0.0 180.0 65.52 −65.52 180.0 −61.22 61.22

B3PW91/6-311G (d, p) 180.0 180.0 0.0 0.0 180.0 180.0 0.0 0.0 180.0 180.0 0.0 180.0 65.54 −65.54 180.0 −61.23 61.23

MPW1PW91/6-311G (d, p) 180.0 180.0 0.0 0.0 180.0 180.0 0.0 0.0 180.0 180.0 0.0 180.0 65.49 −65.49 180.0 −61.18 61.18

Experimental valuea,b,c – – – – –

Ref no. [30,34,35].

spectra of the 2-chloro-4-methylaniline [31]. DFT calculations for BSAME are performed using GAUSSIAN 03W program package on Pentium IV processor personal computer without any constraint on the geometry [32,33]. 4. Results and discussion 4.1. Molecular geometry The molecular structure of the BSAME belongs to CS point group symmetry. The optimized molecular structure of title molecule is obtained from GAUSSAN 03W and GAUSSVIEW programs and they are shown in Fig. 1. The molecule contains SO3 and CH3 connected with benzene ring. The structure optimization zero point vibrational energy of the title compound in LSDA/6311G (d, p), B3LYP/6-311G (d, p), B3PW91/6-311G (d, p) and MPW1PW91/6-311G (d, p) are −366060.9, −373309.9, −377200.9 and −375783.4 J/mol and 87.49, 89.22, 90.15 and 89.81 kcal/mol, respectively. The comparative optimized structural parameters such as bond lengths, bond angles and dihedral angles are presented in Table 1. From the theoretical values, it is found that most of the optimized bond lengths are slightly larger than the experimental values, due to that the theoretical calculations of isolated molecules in gaseous phase and the experimental results of molecules in solid state. Comparing bond angles and lengths of LSDA/B3LYP/B3PW91/MPW1PW91, the values in the B3LYP method are larger than other sets. However, the calculated values from B3PW91/MPW1PW91 method compares well with the experimental data. Inspite of these differences calculated geometrical parameters represent a good approximation and they are the bases for calculating other parameters such as vibrational frequencies and thermodynamics properties. The comparative graphs of bond lengths, bond angles and dihedral angles of BSAME for four sets are presented in Figs. 2–4, respectively. From the theoretical values one can find that most of the optimized bond lengths are larger than the experimental values. This is due to the fact that the theoretical calculations result from isolated molecules in gaseous phase while the experimental results are from molecule in solid state. According to the computed values (B3LYP/6-311G (d, p)), the entire C–C bond lengths ˚ of the benzene ring differ from one another by 0.001 A˚ to 0.004 A. Hence the hexagonal structure of the benzene ring is not affected by a large amount due to the SO3 and CH3 substitutions. The experimental bond length of C–S is 1.767 A˚ [30] nearly coincides with the calculated value from LSDA/6-311G (d, p) method.

The bond length of S O calculated by DFT with LSDA/B3LYP/6˚ respectively. On comparing 311G (d, p) are 1.454 A˚ and 1.456 A, these values with experimental value of 1.430 A˚ [34], it is seen that, the DFT (LSDA/B3LYP/B3PW91/MPW1PW91) overestimates the bond length. The experimental bond length C–H of methyl substitution is 1.090 A˚ which coincides well with the calculated value from MPW1PW91/6-311G (d, p). The experimental C–H bond lengths of the benzene ring 1.080 A˚ nearly coincide with the calculated values from B3LYP/B3PW91/MPW1PW91/6-311G (d, p) basis sets. The observed C–O bond length is found to be 1.346 A˚ [35] whereas the calculated values considerably differ by 1.448, 1.437, 1.447 A˚ in DFT (B3LYP, B3PW91 and MPW1PW91) since the H is replaced by CH3 . The symmetry of the benzene ring is not disturbed to a great extent and is evident by the CCC bond angle C2–C3–C4 ≈ C3–C4–C5 ≈ C4–C5–C6 ≈ 120◦ , C1–C2–C3 ≈ C1–C6–C5 ≈ 118◦ . The value of the bond angle C2–C1–S12 (∼∼122.91◦ ) calculated by B3PW91/6-311G (d, p) is 2.01◦ higher than the experimental value ∼120.90◦ whereas the value of the bond angle C6–C1–S12 (∼115.46◦ cal.) is 2.56◦ lower than the experimental value (∼118.10◦ ). 4.2. Vibrational assignments The BSAME consists of 19 atoms, and belongs to Cs symmetry. Hence the number of normal modes of vibrations for BSAME works to 51. Of the 51 normal modes of vibrations, 34 modes of vibrations are in plane and remaining17 are out of plane. The bands that belong to the in-plane modes are represented as A while the out-of-plane modes as A . Thus the 51 normal modes of vibrations are distributed as  Vib = 34A + 17A . All the 51 fundamental vibrations are active both in Raman scattering and in IR absorption. The harmonic-vibrational frequencies calculated for BSAME at DFT – LSDA/B3LYP/B3PW91/MPW1PW91 levels using the triple split valence basis set along with the diffuse and polarization functions, 6-311G (d, p), observed FT-IR and FT-Raman frequencies for various modes of vibrations are presented in Table 2. Although basis set are marginally sensitive as observed in the DFT values using 6-311G (d, p), reduction in the computed harmonic vibrational frequencies are noted. With out affecting the basic level of calculations, it is customary to scale down the calculated harmonic frequencies in order to get an agreement with the experimental values. The scaled calculated frequencies minimize the root-mean square difference between calculated and experimental frequencies for bands with definite identifications. The descriptions concerning the assignment have also been indicated

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Fig. 3. Comparative graph of bond angle differences between the levels of DFT.

in Table 2. The comparative IR and Raman spectra of experimental and calculated DFT (LSDA/B3LYP/B3PW91/MPW1PW91) are given in Figs. 5 and 6, respectively. 4.3. Computed IR intensity and Raman activity analysis Computed vibrational spectral IR intensities and Raman activities of the BSAME for corresponding wave numbers by DFT methods with LSDA/B3LYP/B3PW91/MPW1PW91 at 6-311G (d, p) basis sets are given in Table 3. The title molecule is a non-polar molecule

with CS point group. Comparison of IR intensity and Raman activity calculated by DFT with LSDA/B3LYP/B3PW91/MPW1PW91 at 6-311G (d, p) methods with experimental values shows the variation of IR intensities and Raman activities. In the case of IR intensity, the values of B3LYP/B3PW91 at 6-311G (d, P) are found to be higher than LSDA/MP1PW91 at 6-311G (d, P) whereas in the case of Raman activity the effect is reversed. The similar effect was also noticed in the earlier paper [36]. The comparative plots of IR intensities and Raman activities for four sets are presented in Figs. 7 and 8, respectively.

Fig. 4. Comparative graph of dihedral angle differences between the levels of DFT.

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Fig. 5. Experimental [A], calculated [B], [C], [D] and [E] FTR spectra of benzenesulfonic acid methylester.

Fig. 6. Experimental [A], calculated [B], [C] and [E] FT-Raman spectra of benzenesulfonic acid methylester.

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Table 2 Observed and LSDA/6-311G (d, p), B3LYP/6-311G (d, p), B3PW91/6-311G (d, p) and MPW1PW91/6-311G (d, p) level calculated vibrational frequencies of benzenesulfonic acid methyl ester. S. no.

Symmetry species C1

Observed frequency

Calculated frequency (cm−1 ) with LSDA/6-311G (d, p)/B3LYP/6-311G (d, p)

Calculated frequency (cm−1 ) with B3PW91/6-311G (d, p)/ MPW1PW91/6-311G (d, p)

FT-IR

FT-Raman

Unscaled value

Scaled value

Unscaled value

Scaled value

1 2 3 4 5 6



A A A A A A

3070w 3065w 3060w – – 3020w

3070vs – 3060vs 3040w 3030w –

3354/3327 3345/3326 3343/3322 3339/3318 3334/3316 3329/3310

3062/3061 3053/3060 3052/3056 3048/3052 3020/3050 3016/3045

3360/3355 3347/3353 3343/3349 3340/3346 3335/3343 3329/3336

3061/3053 3049/3051 3045/3047 3042/3044 3038/3042 3032/3035

7

A

3010w

–

3323/3302

3010/3037

3322/3328

3026/3028

8



A

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

A A A A A A A A A A A A A A A A A A A A A A  A A A A  A  A  A  A A  A A A A

44 45 46 47 48

(C–H)  (C–H)  (C–H)  (C–H)  (C–H)  CH3 (C–H)



CH3 (C–H)

 2960w

2960m

3240/3229

2958/2970

3248/3248

2958/2955

CH3 (C–H)

 1590w 1580w – 1450vs 1370vs 1360vs 1340vs 1290w 1180vs 1170vs 1165vs 1160vs 1100w 1090w 1080w – 1020s 1000vs 990vs 980vs 970vs – 930w 840w 800vs 780vs 710vs 690vs 590vs 580vs 530w 480m 380vs 370vs 330vs

1590vs 1580vs 1490w 1450w – 1360w – – 1180vs 1170vs 1165vs 1160vs 1100vs – – 1030vs – 1000vs – – – 940w – 840w – 780m 710vs – 590vs 580m – 480w – 370s 330vs

1552/1592 1541/1586 1448/1495 1402/1484 1382/1466 1372/1448 1350/1444 1306/1322 1242/1279 1227/1231 1126/1178 1112/1152 1079/1150 1074/1138 1066/1116 1044/1079 1030/1067 997/1029 992/1025 982/1004 880/957 850/930 785/870 712/780 697/743 683/707 639/655 602/651 580/621 566/605 493/503 458/486 408/403 397/398 343/351

1598/1592 1587/1586 1491/1495 1444/1446 1382/1370 1372/1354 1350/1350 1306/1288 1180/1195 1165/1169 1160/1178 1145/1152 1111/1107 1106/1095 1097/1074 1044/1039 1030/1027 997/990 992/987 982/969 968/966 935/939 902/878 818/826 801/787 785/750 734/694 692/690 597/598 582/582 507/533 471/486 387/376 377/372 325/328

1600/1605 1591/1599 1536/1495 1475/1485 1468/1466 1448/1447 1437/1443 1316/1317 1292/1289 1239/1235 1195/1178 1154/1153 1145/1150 1140/1138 1127/1119 1093/1082 1070/1070 1038/1030 1028/1028 1006/1006 954/964 935/940 878/877 787/787 734/746 708/715 663/658 658/656 619/619 589/609 525/512 478/494 439/412 415/405 363/352

1600/1605 1591/1599 1489/1495 1445/1450 1370/1368 1351/1350 1341/1346 1289/1286 1177/1202 1156/1172 1159/1178 1154/1153 1110/1091 1063/1079 1051/1061 1020/1026 998/1015 1006/1006 997/1004 975/983 992/964 935/940 913/939 834/838 778/794 750/790 702/722 697/704 606/612 589/577 525/512 478/494 399/384 378/377 330/328

A A A

310vs 300vs 260vs

– – 260w

293/283 266/273 225/246

293/300 301/289 258/261

309/281 281/281 244/248

309/297 297/281 258/262

A A

190vs 100w

190w –

165/122 111/90

170/129 111/95

186/141 146/99

197/149 133/105



Vibrational assignments

(C C)  (C C)  (C C)  (CH3 ) ␣ (C–C)  (C–C)  (S O)  as (C–H) ␦ (C–H) ␦ (C–H) ␦ (C–H) ␦ (S O)  s (C–H) ␦ (C–H) ␦ (C–H) ␦ (O–CH3 )  (C–H) ␦ (C–H) ␥ (C–H) ␥ (C–H) ␥ (C–H) ␥ (C–H) ␥ (C–S)  (C–H) ␥ (C–H) ␥ (C–H) ␥ (CCC) ␦ (CCC) ␦ (CCC) ␦ (S O) ␦ (CCC) ␥ (C–S) ␦ (CCC) ␥ (CCC) ␥ (S–O–CH3 ) ␦ (O–CH3 ) ␦ (C–S) ␥ (S–O–CH3 ) ␥ (O–CH3 ) ␶ (CH3 ) ␶

VS – very strong; S – strong; m – medium; w – weak; as – asymmetric; s – symmetric;  – stretching; ı – in plane bending; ␥ – out plane bending; ␣ – deformation; ␶ – twisting.

4.4. Computed vibrational frequency analysis The comparative graph of calculated vibrational frequencies by DFT methods LSDA/6-311G (d, p), B3LYP/6-311G (d, p), B3PW91/6311G (d, p) and MPW1PW91/6-311G (d, p) basis sets for the BSAME are given in Fig. 9. From the figure, it is found that the calculated (unscaled) frequencies by LSDA/B3LYP/ B3PW91/MPW1PW91 with 6-311G (d, p) basis sets are closer to the experimental frequencies. This observation is in line with our earlier work [37]. The standard deviation (SD) calculation made between experimental

and computed frequencies DFT for the BSAME is presented in Table 4. According to the SD, the computed frequency deviation decreases in going from B3PW91/6-311G (d, p) to LSDA/6-311G (d, p) to MP1PW91/6-311(d, p) to B3LYP/6-311(d, p). The deviation ratio between LSDA/6-311G (d, p) and B3LYP/6-311G (d, p) is 1.05, B3LYP/6-311G (d, p) and B3PW91/6-311G (d, p) is 0.99 and HF/6-311G (d, p) and MPW1PW91/6-311G (d, p) is 1.004. It is also observed that the calculated frequencies by B3LYP/6-311G (d, p) basis sets are closer to the experimental frequencies than other basis sets in DFT method.

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175

Table 3 Comparative values of IR intensities and Raman activities between LSDA/6-311G (d, p), B3LYP/6-311 G (d, p), B3PW91/6-311G (d, p) and MPW1PW91/6-311G (d, p) of benzenesulfonic acid methyl ester. Frequency

3070 3065 3060 3040 3030 3020 3010 2960 1590 1580 1490 1450 1370 1360 1340 1290 1180 1170 1165 1160 1100 1090 1080 1030 1020 1000 990 980 970 940 930 840 800 780 710 690 590 580 530 480 380 370 330 310 300 260 190 100

Calculated with LSDA/6-311G (d, p)

Calculated with B3LYP/6-311G (d, p)

Calculated with B3PW91/6-311G (d, p)

Calculated with MPW1PW91/6-311G (d, p)

IR intensity (Ai)

Raman activity (I)

IR intensity (Ai)

Raman activity (I)

IR intensity (Ai)

Raman activity (I)

IR intensity (Ai)

Raman activity (I)

2.53 2.27 0.35 0.53 0.83 1.68 0.27 24.4 1.48 0.08 9.33 2.36 23.6 2.25 8.44 0.71 195.0 2.79 59.6 80.4 0.73 1.61 15.3 16.5 16.6 53.1 6.13 2.61 0.03 0.26 0.81 97.1 22.2 0.39 96.7 13.4 38.2 73.0 34.9 0.83 24.0 4.93 4.90 2.44 5.50 3.81 0.42 1.17

41.8 340.5 39.6 34.3 77.7 91.3 22.9 197.0 10.4 31.6 9.29 2.96 2.62 7.51 4.79 2.16 11.2 0.36 28.9 32.9 3.91 6.12 3.71 15.8 6.65 2.26 11.4 27.9 0.08 0.46 0.48 2.84 0.45 0.21 10.2 4.48 1.37 5.52 0.87 7.51 0.91 3.19 3.31 1.43 5.51 1.31 0.28 4.21

7.08 7.30 2.07 8.45 1.24 4.79 0.41 32.8 0.32 0.27 14.9 6.93 11.1 1.39 15.6 2.01 1.13 221.6 0.67 20.5 96.2 0.21 66.4 2.38 26.7 5.11 164.3 6.81 0.00 0.12 0.29 0.27 132.6 4.85 148.7 56.3 14.3 59.5 43.5 4.99 4.19 0.29 9.20 2.51 0.04 14.4 0.11 3.69

223.2 196.4 4.17 36.4 59.3 109.8 33.2 138.8 17.0 23.3 8.20 0.22 13.8 3.95 1.61 0.36 1.13 6.33 2.76 4.02 5.0 1.55 37.0 2.50 1.81 1.68 5.11 43.3 0.03 0.00 0.03 0.26 3.72 0.09 12.9 0.39 5.82 3.80 0.45 11.9 0.77 0.55 3.23 7.61 0.07 2.74 5.55 1.06

4.59 5.70 4.83 0.63 2.07 3.14 0.07 30.8 1.14 0.47 5.25 2.74 6.54 8.19 12.7 1.70 0.29 226.0 2.57 0.77 0.42 2.15 154.4 4.16 35.7 91.0 3.25 3.06 0.00 0.19 0.73 0.86 116.8 2.20 61.9 110.7 14.8 86.0 25.9 0.84 12.7 1.06 4.05 1.44 5.71 3.10 1.05 4.10

38.7 292.5 72.3 28.9 68.7 98.9 25.8 169.3 16.8 23.2 7.98 1.87 8.11 4.83 0.40 0.32 1.29 8.74 1.70 3.16 3.75 2.20 47.2 0.25 3.82 2.68 12.2 33.5 0.34 0.86 0.50 0.10 1.82 0.10 0.37 10.8 5.73 4.09 0.85 6.99 0.67 4.07 2.84 1.43 6.39 1.25 0.31 0.88

3.70 7.82 0.98 7.06 0.49 4.02 0.43 30.1 0.21 0.37 15.8 6.72 11.8 12.8 4.99 2.09 1.17 231.3 1.05 119.8 15.7 0.14 60.1 3.74 28.0 8.38 158.0 6.33 0.0 0.12 0.27 0.26 143.9 4.64 145.3 59.5 19.7 52.5 46.5 6.11 4.09 0.01 7.92 0.04 2.54 13.6 0.08 3.67

86.4 315.3 5.41 34.1 56.0 102.6 30.0 136.8 15.6 23.1 7.84 0.20 13.3 1.48 3.85 0.44 1.03 6.04 2.70 5.55 4.11 1.53 35.7 2.56 1.57 3.80 5.84 39.3 0.04 0.0 0.05 0.11 3.89 0.06 12.5 0.28 5.08 4.22 0.47 11.9 0.99 0.34 3.18 0.05 7.21 2.68 5.51 1.02

4.5. Frequency estimation analysis The ideal estimation of frequencies by DFT (LSDA/B3LYP/B3PW91/MPW1PW91) methods are presented in Table 5. The frequencies calculated by various basis sets perfectly coincide with the experimentally observed values of FT-IR and FT-Raman with out scaling. While comparing the estimation of frequencies by various sets of the DFT method, the LSDA/6-311G (d, p) basis set estimate accurately more number of frequencies

than other sets. The estimated frequencies belong to both finger print and functional group regions. The LSDA set gives the frequencies accurately for C–C, S–O, C–H in-plane and out-of-plane bending and O–CH3 vibrations whereas the B3LYP set yields the frequencies accurately for C–C and C–H in-plane bending vibrations. The B3PW91 set offers the frequencies accurately for C–C C–H in-plane bending and CCC vibrations and MPW1PW91 set gives the frequencies accurately for C–C, S–O, C–H in-plane and out-of-plane bending, CCC and S–OCH3 vibrations. Certain set

Table 4 Standard deviation of frequencies by DFT (LSDA/B3LYP/B3PW91/MPW1PW91) at 6-311G (d, p) basis sets. S. no.

Basic set levels

1 2 3 4

Experimental LSDA/6-311(d, p) B3LYP/6-311(d, p) B3PW91/6-311(d, p) MP1PW91/6-311(d, p)

Total values 59,770 61,084 62,409 62,933 62,789

Average

Standard deviation

Deviation ratio

1245.2 1272.5 1300.1 1311.1 1308.1

– 58.07 55.02 58.26 57.79

– – 1.05 0.99 1.004

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Table 5 Ideal estimation of calculated frequencies by DFT (LSDA/B3LYP/B3PW91/MPW1PW91) at 6-311G (d, p) basis sets. S. no.

Basis sets LSDA/6-311 (d, p)

1 2 3 4 5 6 7 8 9 10 11

1382 1372 1350 1306 1044 1030 997 992 982 293 111

Assigned frequencies

B3LYP/6-311 (d, p)

(C–C)  (C–C)  (S O)  as (C–H) ␦ (O–CH3 )  (C–H) ␦ (C–H) ␥ (C–H) ␥ (C–H) ␥ (O–CH3 ) ␦ (CH3 ) ␶

Fig. 7. Comparative graph (LSDA/B3LYP/B3PW91/MPW1PW91).

of

(C C)  (C C)  (C C)  (C–H) ␦ (C–H) ␦ (CCC) ␥ – – – – –

1592 1586 1495 1178 1152 486 – – – – –

IR

Assigned frequencies

intensities

by

DFT

of frequencies calculated by B3PW91 and MPW1PW91coincides accurately with the experimentally observed values. 4.5.1. C–H vibrations For all the aromatic compounds the carbon–hydrogen stretching vibrations are observed in the region 3000–3100 cm−1 [38,39]. In the present study, five adjacent hydrogen atoms left around the ring and give rise to five C–H stretching modes, five C–H

Fig. 8. Comparative graph (LSDA/B3LYP/B3PW91/MPW1PW91).

of

Raman

activities

by

DFT

B3PW91/6-311 (d, p) 1600 1591 1154 935 589 525 478 309 – – –

Assigned frequencies (C C)  (C C)  (C–H) ␦ (C–H) ␦ (CCC) ␥ (CCC) ␥ (CCC) ␥ (O–CH3 ) ␦ – – –

MP1PW91/6-311 (d, p) 1605 1599 1495 1178 1153 964 940 512 494 281 –

Assigned frequencies (C C)  (C C)  (C C)  (C–H) ␦ (C–H) ␦ (C–H) ␥ (C–H) ␥ (CCC) ␥ (CCC) ␥ (S–OCH3 ) ␥ –

Fig. 9. Comparative graph of experimental and computed frequencies by DFT.

in-plane bending and five C–H out-of-plane bending vibrations which corresponds to modes of C2–H7, C3–H8, C4–H9, C5–H10 and C6–H11 units. For the BSAME, the C–H stretching vibrational bands are observed at 3070, 3065, 3060, 3040 and 3030 cm−1 . The C–H in-plane bending and C–H out-of-plane bending vibrations are normally found in the range 1000–1300 cm−1 and 750–1000 cm−1 , respectively, in the aromatic compounds [40,41]. For the BSAME, the vibrational frequencies are assigned at 1290, 1180, 1170, 1165 and 1100 cm−1 for C–H in-plane bending and the bands found to 1000, 990, 980, 970 and 940 cm−1 are assigned to C–H out-of-plane bending. In general, all the assigned C–H vibrations (stretching, in-plane and out-of-plane bending) are not affected by the substitution in the ring and are in good agreement with theoretically calculated values by DFT (LSDA/B3LYP/B3PW91/MPW1PW91). 4.5.2. Methyl group vibrations In aromatic methoxy compounds, the C–H stretching vibrations of the methyl group are normally falling in the region 2840–2975 cm−1 [42,43]. There are two strong bands at 3020 and 3010 cm−1 and a strong band around 2890 cm−1 corresponding to asymmetric and symmetric stretching modes, respectively [44,45]. In the present molecule, two bands are assigned in FT-IR at 3020 and 3010 cm−1 and the other medium band is found at 2960 cm−1 . The first two bands are above the expected range and is purely due to the SO2 . The theoretically computed values by B3LYP/6-311G (d, p) method for CH3 stretching reasonably coincide with FT-IR experimental values.

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The C–H in-plane and out-of-plane bending vibrations for methyl group in the BSAME are assigned to 1090, 1080 and 1020 cm−1 and 840, 800 and 780 cm−1 , respectively. These assignments are in line with the literature values [46,47] and nearly coincides with the calculated frequencies by LSDA/B3LYP/B3PW91/MPW1PW91/6-311G (d, p). The asymmetric deformation of CH3 group is usually observed at around 1450 cm−1 for methyl substituted benzenes [48,49]. As expected, very strong intensity band appeared at 1450 cm−1 in FT-IR and FT-Raman spectra are due to CH3 asymmetric deformation vibration. The theoretically calculated values by B3PW91/MPW1PW91/6-311G (d, p) coincide very well with the experimental value. 4.5.3. C C vibrations Generally the C C stretching vibrations in aromatic compounds are seen in the region of 1430–1650 cm−1 . According to Socrates [50], the presence of conjugate substituent such as C C causes a heavy doublet formation around the region 1625–1575 cm−1 . The six ring carbon atoms undergo coupled vibrations which are known as skeletal vibrations give a maximum of four bands in the region 1660–1420 cm−1 . As predicted in the earlier references [51], the prominent peaks at 1590, 1580 and 1490 cm−1 are due to strong C C stretching and 1370 and 1360 cm−1 are due to strong C–C skeletal vibrations for the title compound. The peaks at 1590, 1580 and 1490 cm−1 and the peaks at 1370 and 1360 cm−1 are due to quadrant and semicircle stretching of C C bonds, respectively [52]. These four peaks confirm that the compound is aromatic in nature [53]. The peaks are assigned at 690, 680 and 660 cm−1 due to C–C–C in-plane bending vibrations and the peaks at 570, 530 and 510 cm−1 are due to C–C–C out-of-plane bending vibrations. Except C–C stretching vibrations, all the assignments are coherent with the literature data [54]. The C–C vibrations are pulled slightly to the lower region and are purely due to the slight-breakdown of hexagonal ring by the substitutions. 4.5.4. SO2 vibrations The symmetric and asymmetric SO2 stretching vibrations occur in the region 1125–1150 and 1295–1330 cm−1 [41]. The intense bands appearing at 1418 cm−1 and 1217 cm−1 in FT-IR and 1414 cm−1 and 1228 cm−1 in FT-Raman can be attributed to the SO2 anti-symmetric and symmetric stretching fundamental modes for sulfa moil fluoride substance [55]. In the present compound, the SO2 asymmetric and symmetric stretching vibrations are recorded at 1340 cm−1 and 1160 cm−1 , respectively. In reference to the literature, the observed values are slightly deviated to the expected region. This is purely due to the replacement of OH by OCH3 . The SO2 in-plane and out-of-plane bending vibrations for title molecule are found at 590 cm−1 and 370 cm−1 , respectively. The theoretically computed frequencies for SO2 vibrations by B3PW91/6-311G (d, p) method shows excellent agreement with recorded spectrum as well as with literature values. 4.5.5. O–CH3 vibrations The O–CH3 stretching mode is normally assigned in the region 1000–1100 cm−1 [56–60]. In this compound, a strong band is found at 1030 cm−1 for O–CH3 stretching vibration. The theoretically computed value by LSDA/6-311G (d, p) method for O–CH3 stretching is coincides with FTR experimental and literature values. The O–CH3 angle bending mode is assigned at 310 cm−1 by Owen and Hester [61]. Ramana Rao et al. [62] has proposed assignment for this mode in the region 300–670 cm−1 . In accordance with above a band is assigned to 330 cm−1 from the theoretically calculated value by LSDA/6-311G (d, p) as S–O–CH3 angle bending mode. This assignment exactly coincides with the 330 cm−1 band observed in the FT-IR spectrum. Varsanyi [63] has proposed assignment for out-ofplane mode of the O-CH3 group at 100 cm−1 for anisole. In the title

177

molecule, the S–O–CH3 out-of-plane bending vibration is assigned at 190 cm−1 . According to the literature, this assignment is agreed well. 4.5.6. C–S stretching vibrations The C-S stretching bands are usually observed in the range 670–930 cm−1 [64,65] with a moderate intensity. For BSAME, the C–S stretching mode is observed at 930 cm−1 and agrees well with the computed value 939 cm−1 from MPW1PW91/6-311G (d, p). The C–S in-plane and out-of-plane bending vibrations bands are expected in the regions 600–420 cm−1 and 420–320 cm−1 , respectively [66]. In the present work, the C–S in-plane and out-of-plane bending vibrations are assigned to 480 cm−1 and 300 cm−1 , respectively. All the C–S vibrational bands of the title compound are inline with the literature values and nearly in agreement with the computed values by B3PW91/MPW1PW91/6-311G (d, p) basis sets. 5. Conclusion Based on the calculations DFT with LSDA/B3LYP/B3PW91/ MPW1PW91/6-311G (d, p) levels, complete vibrational properties of BSAME have been investigated by FT-IR and FT-Raman spectroscopies, respectively. The optimized structural parameter such as bond length, bond angle and dihedral angles are also calculated and are compared among HF and DFT methods. The assignments of the fundamental frequencies are confirmed by the qualitative agreement between the calculated and observed frequencies. The C–H stretching, in-plane bending and out-of-plane bending bands and C C stretching vibrational frequencies are observed well within the expected range compared to the literature values. Among methyl C–H stretching vibrations, only some are expected in asymmetric range while others in symmetric range. But in the present case, all the observed bands for stretching lay in asymmetric range. These shows the vibrations of methyl group are enhanced up by SO2 . The SO2 vibrations in the title molecule are remarkably pure modes and the significant vibrational interactions with other fundamentals are also observed. Out of the 51 normal modes of vibrations, only 48 vibrations could be assigned since the last three are below in the observed range. References [1] J.F. King, S. Patai, Z. Rappoport, The Chemistry of Sulphonic Acids, Esters and Their Derivatives, Wiley, Chichester, 1991, p. 249. [2] H.G.M. Edwards, D.R. Brown, J.A. Dale, S. Plant, Vib. Spectrosc. 24 (2000) 213–218. [3] P.F. Siril, A.D. Davison, J.K. Randhawa, D.R. Brown, J. Mol. Catal. A: Chem. 267 (2007) 72–78. [4] H. Widdecke, in: D.C. Sherington, P. Hogde (Eds.), Synthesis and Separations Using Functional Polymers, Wiley, New York, 1998, pp. 149–155. [5] C.E. Harland, Ion Exchange, 2nd ed., Royal Society of Chemistry, London, 1994. [6] A. Corma, Chem. Rev. 95 (1995) 559–563. [7] J.H. Clark, D.J. Macqquarrie, Chem. Soc. Rev. 25 (1996) 310–315. [8] M.A. Harmer, Q. Sun, Appl. Catal. A 221 (1/2) (2001) 45–48. [9] A. Chakraborthy, M.M. Sharma, React. Funct. Polym. 20 (1993) 1–5. [10] M. Harold, On Food and Cooking, Scribner, New York, 2003. [11] W. Riemenschneider, H.M. Bolt, “Esters Organic” Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. [12] G.E. Taylor, M. Gosling, A. Pearce, J. Chromatogr. A 1119 (2006) 231–237. [13] S. Rayne, K. Forest, J. Mol. Struct. (Theochem.) 941 (2010) 107–118. [14] M. Karabacak, M. Cinar, A. Coruh, M. Kurt, J. Mol. Struct. (Theochem.) 919 (2009) 26–33. [15] R.G. Parr, W. Yang, Density-Functional Theory of Atoms and Molecules, Oxford University Press, 1989. [16] S. Sadhukhan, D. Munoz, C. Adamo, G.E. Scuseria, Chem. Phys. Lett. 306 (1999) 83–87. [17] I.S. Lim, G.E. Scuseria, Chem. Phys. Lett. 460 (2008) 137–140. [18] T. Cai, H. Han, Y. Yua, T. Gao, J. Du, L. Hao, Physica B 404 (2009) 89–94. [19] Z. Zhengyu, Du. Dongmei, J. Mol. Struct. (Theochem.) 505 (2000) 247–252. [20] Z. Zhengyu, Fu. Aiping, Du. Dongmei, Int. Quant. Chem. 78 (2000) 186–189. [21] A.D. Becke, Phys. Rev. A 38 (1988) 3098–3101. [22] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785–790. [23] A.D. Becke, J. Chem. Phys. 98 (1993) 5648–5652.

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