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Scaled quantum chemical studies on the vibrational spectra of 4-bromo benzonitrile
Spectrochimica Acta Part A 71 (2009) 1810–1813
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Scaled quantum chemical studies on the vibrational spectra of 4-bromo benzonitrile V. Krishnakumar a,∗ , N. Surumbarkuzhali b , S. Muthunatesan c a
Department of Physics, Periyar University, Salem 636 011, India Department of Physics, Government Polytechnic College, Krishnagiri 635001, India c Department of Physics, Government Arts College (Autonomous), Kumbakonam 612001, India b
a r t i c l e
i n f o
Article history: Received 20 December 2007 Accepted 24 June 2008 Keywords: 4-Bromo benzonitrile Density functional theory Vibrational spectra
a b s t r a c t The vibrational spectra of 4-bromo benzonitrile have been reported. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-311+G basis set combination and were scaled using various scale factors which yielded a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound which showed excellent agreement with the observed spectra. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Benzonitrile, derived mainly from benzoic acid reaction with lead thiocyanate by heating, is a clear liquid; boils at 191 ◦ C. It reacts violently with strong acids to produce toxic hydrogen cyanide. It decomposes on heating, producing very toxic fumes, hydrogen cyanide, nitrous oxides [1]. Benzonitrile is used as a solvent and chemical intermediate for the synthesis of pharmaceuticals, dyestuffs and rubber chemicals through the reactions of alkylation, condensation, esterification, hydrolysis, halogenation or nitration. Benzonitrile and its derivatives are used in the manufacture of lacquers, polymers and anhydrous metallic salts as well as intermediates for pharmaceuticals, agrochemicals, and other organic chemicals. Due to greater pharmaceutical importance, 4-bromo benzonitrile has been taken for the present study. The complete vibrational analysis of 4-bromo benzonitrile was performed by combining the experimental and theoretical information using Pulay’s density functional theory (DFT)-based scaled quantum chemical approach [2]. 2. Experimental details The fine sample of 4-bromo benzonitrile was obtained from Lancaster chemical company, UK, and used as such for the spectral measurements. The FTIR spectrum of the title compound
∗ Corresponding author. E-mail address: vkrishna [email protected] (V. Krishnakumar). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.06.037
was recorded using PerkinElmer spectrum RX1 spectrophotometer equipped with He–Ne laser source in the region 100–4000 cm−1 using KBr and polyethylene pellets. The FT-Raman spectra were recorded on Bruker IFS-66V model interferometer equipped with an FRA-106 FT-Raman accessory in the 3500–100 cm−1 Stokes region using the 1064-nm line of Nd: YAG laser for excitation operating at 200 mW power. The reported wave numbers are believed to be accurate within ±1 cm−1 . 3. Computational details The quantum chemical calculations were performed by applying DFT method using the Gaussian 98W program [3] using the Becke 3-Lee-Yang-Parr (B3LYP) functional [4] supplemented with the standard 6-311+G** basis set [5,6]. The Cartesian representation of the theoretical force constants has been computed at the fully optimized geometry by assuming CS point group symmetry. Scaling of the force field was performed according to the SQM procedure [7,8] using selective scaling in the natural internal coordinate representation [2,8]. Transformations of the force field and the subsequent normal coordinate analysis including the least squares refinement of the scaling factors, calculation of total energy distribution (TED) and prediction of IR and Raman Intensities were done on a PC with the MOLVIB program written by Sundius [9,10]. The TED elements provide a measure of each internal coordinate’s contributions to the normal coordinate. For the plots of simulated IR and Raman spectra, pure Lorentzian band shapes were used with a bandwidth of 10 cm−1 . The prediction of Raman intensities was carried out by following the
V. Krishnakumar et al. / Spectrochimica Acta Part A 71 (2009) 1810–1813
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Table 1 Optimized geometrical parameters of 4-bromo benzonitrile Bond length
Value (Å)
Bond angle
Value (◦ )
C1–C2 C2–C3 C3–C4 C4–C5 C5–C6 C1–C7 C2–H8 C3–H9 C4–Br10 C5–H11 C6–H12 C1–H13
1.4047 1.3912 1.3952 1.3952 1.3913 1.4336 1.0845 1.0837 1.9054 1.0837 1.0845 2.5969
C1–C2–C3 C2–C3–C4 C3–C4–C5 C4–C5–C6 C2–C1–C7 C3–C2–H8 C4–C3–H9 C5–C4–Br10 C6–C5–H11 C1–C6–H12 C2–C1–N13 C6–C5–C4–Br10 C3–C2–C1–N13
120.1313 119.2682 121.3755 119.2674 120.0864 120.1224 120.1964 119.311 120.539 120.539 120.539 180 180
For numbering of atoms refer Fig. 1. Fig. 1. Molecular model of 4-bromo benzonitrile along with numbering of atom.
4.2. Vibrational analysis of and theoretical prediction of spectra procedure outlined below. The Raman activities (Si ) calculated by the Gaussian 98W program and adjusted during the scaling procedure with MOLVIB were converted to relative Raman intensities (Ii ) using the following relationship derived from the basic theory of Raman scattering [11–13]: Ii =
f (0 − i )4 Si i [1 − exp(−hci /KT )]
(1)
where 0 is the exciting frequency (cm−1 units); i the vibrational wave number of the normal mode; h, c and k are the universal constants, and f is the suitably chosen common normalization factor for all the peak intensities.
The 33 normal modes of 4-bromo benzonitrile are distributed amongst the symmetry species as vib = 23A (in-plane) + 10A (out-of-plane) In agreement with Cs symmetry, all the vibrations are active both in Raman scattering and infrared absorption. The detailed vibrational assignments of fundamental modes of 4-bromo benzonitrile along with the calculated IR, Raman intensities and normal mode descriptions were reported in Table 4. For visual comparison, the observed and simulated FTIR and laser Raman spectra were presented in Figs. 2 and 3, respectively. Root mean square (RMS) values of frequencies were obtained using the following expression:
n 1 exp 2 RMS = (icalcu − i )
4. Results and discussion 4.1. Molecular geometry
n−1
The molecular structure of the 4-bromo benzonitrile having Cs point group of symmetry is shown in Fig. 1. The global minimum energy was obtained by the DFT structure optimization and was calculated as −2895.60183060 hartrees. The most optimized structural parameters were also calculated and they were depicted in Table 1.
(2)
i
The RMS error of frequencies (unscaled/B3LYP/6-311+G**) obtained for 4-bromo benzonitrile was found to be 94.62 cm−1 . In order to reproduce the observed frequencies, refinement of scaling factors was applied and optimized via least square refinement algorithm which resulted a RMS deviation of 7.27 cm−1 .
Table 2 Definitions of internal coordinates of 4-bromo benzonitrile No.
Symbol
Type
Definition
Stretching 1–4 5 6 7 8–13
ri Ri Qi qi Ti
C–H C–C (aromatic) C–Br C–N C–C (ring)
C2–H8, C3–H9, C4–H11, C5–H12 C1–C7 C4–Br10 C1–N13 C1–C2, C2–C3, C3–C4, C4–C5, C5–C6, C6–C1
Bending 14–21 22–27 28–29 30–31 32–33
ˇi i i ˛i i
C–C–H C–C–C (ring) C–C–C (aromatic) C–C–Br C–C–N
C3–C2–H8, C1–C2–H8, C4–C3–H9, C2–C3–H9, C6–C5–H11, C4–C5–H15, C1–C6–H12, C5–C6–H12 C1–C2–C3, C2–C3–C4, C3–C4–C5, C4–C5–C6, C5–C6–C1, C6–C1–C2 C7–C1–C2, C7–C1–C6 C5–C4–Br10, C3–C4–Br10 C2–C1–N13, C6–C1–N13
C–H C–Ca C–Br C–N ring
H8–C2–C3–C1, H9–C3–C4–C2, H11–C5–C6–C4, H12–C6–C1–C5 C7–C1–C2–C6 Br10–C4–C5–C3 N13–C1–C2–C6 C1–C2–C3–C4, C2–C3–C4–C5, C3–C4–C5–C6, C4–C5–C6–C1, C5–C6–C1–C2, C6–C1–C2–C3
Out-of-plane bending 34–37 ωi 38 ϕi 39 i 40 i 41–46
i For numbering of atoms refer Fig. 1.
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V. Krishnakumar et al. / Spectrochimica Acta Part A 71 (2009) 1810–1813
Table 3 Definition of local symmetry coordinates for 4-bromo benzonitrile No. (i)
Symbola
Definitionb
1–4 5 6 7 8–13 14–17
CH CC (nitrile) C Br CN CC (Ring) bCH
18–20
Rtrigd Rsymd R asymd bCC bCBr bCN CH CC CBr CN tRsym tRasym tRtrigd
r1 , r2 , r3 , r4 R5 Q6 q7 T8 , T9 , T10 , T11 √, T12 , T13 √ (ˇ14 −√ˇ15 )/ 2, (ˇ16 −√ˇ17 )/ 2, (ˇ18 − ˇ19 )/ 2, (ˇ20 − ˇ21 )/ 2 √ (22 − 23 + 22 − 24 + 26 − 27 )/ 6 √ (−22 − 23 + 224 − 25 + 26 − 227 )/ 12 ( 22 − 23 +√25 − 26 )/2 (28 − 29 )/ √2 (˛30 − ˛31 )/√ 2 (32 − 33 )/ 2 ω34 , ω35 , ω36 , ω37 ϕ38 39 40 ( 41 − 42 + 44 − 45 )/2 √ (− 41 + 2 42 − 43 − 44 + 2 45 − √ 46 )/ 12 ( 41 − 42 + 43 − 44 + 45 − 46 )/ 6
21 22 23 24–27 28 29 30 30–33
a b
These symbol are used for description of normal modes by TED in Table 4. The internal coordinates used here are defined in Table 2.
4.2.1. C–H vibrations The aromatic organic compounds always have C–H stretching vibrations in the region 3000–3100 cm−1 which is the character-
Fig. 2. Comparison of observed and calculated FTIR 4-bromo benzonitrile: (a) observed and (b) calculated with B3LYP/6-311+G**.
istic region for the ready identification of C–H vibrations. These vibrations are not found to be affected due to the nature and position of the substituents. The FTIR band at 3086, 3064 and 3047 cm−1 and Raman band at 3076 cm−1 are assigned to C–H stretching vibrations. The C–H bending vibrations are usually occurring in the region 1465–1281 cm−1 [14]. As the C–C stretching vibrations are shifting to the lower wave numbers, C–H bending vibrations are dominating in this region. The assignments of in plane and out of plane C–H bending vibrations are as shown in Table 4.
Table 4 Observed and B3LYP/6–311+G** level calculated vibrational frequencies (cm−1 ) of 4-bromo benzonitrile No.
1 2 3 4 5 6 7 8 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
Symmetry species
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
Observed frequency (cm−1 )
Calculated frequency (cm−1 ) with B3LYP/6-311+G** force field
IR
Unscaled
Scaled
IRa (Ai )
Ramanb (Ii )
3230 3229 3214 3213 2350 1644 1608 1526 1436 1332 1329 1226 1205 1135 1090 1028 986 986 852 850 785 732 652 565 557 546 444 417 274 263 229 134 80
3076 3075 3061 3060 2229 1622 1574 1563 1462 1389 1277 1240 1198 1149 1072 1010 977 970 858 836 731 731 655 563 547 545 434 406 278 264 232 128 80
0.008 1.349 0.7 0.959 32.033 31.321 0.330 54.697 10.659 0.388 2.135 5.197 1.751 1.475 43.167 30.805 0.000 0.001 37.197 0.000 6.055 0.870 0.065 20.677 0.014 9.208 0.060 0.000 1.006 0.153 2.887 6.698 4.163
219.77 3.539 89.938 19.384 536.156 166.249 1.125 0.865 0.137 1.158 0.001 24.978 62.151 0.048 33.803 3.473 2.894 0.001 0.894 5.387 18.968 0.315 3.640 2.314 2.657 0.422 4.153 0.005 5.830 2.099 0.005 2.618 0.930
3086 – 3064 3047 1608 1563 1563 1465 1387 1281 1256
Raman 3076 – – 2229 – – –
1198 1161 1070 1015 986 964 868 825 774 722 653 565 545 544 434 417 279 263 229 131 86
TED (%) among type of internal coordinatesc
CH(99) CH(99) CH(99) CH(99) CN(87), CCasym(12) CC(53), bCH(35), Rtrigd(9) CC(61), bCH(26), Rsym(9) bCH(71), CC(26) bCH(60), CC(34) bCH(71), CC(21) CC(94) bCH(62), CC(36) CCasym(41), CC(26), bCH(10), Rasymd(17) CC(52), bCH(40) CC(66), CBr(22), bCH(8) Rsymd(60), Rtrigd(9), CC(22), CBr(6) CH(75), tRsymd(20) CH(92), tRsymd(8) CH(70), tRsymd(12), CCa (10), CBr(6) CH (100) Raymd(29), Rtrigd(12), CC(28), CCa (16), CBr(9) tRsym(66), CCa (16), CBr(13) Rasymd(61), bCCa (17), CC(15) tRasym(31) Rsymd(38), bCCaym(35), bCCN(18), CC(6) CBr(34), Rsymd(32), CCa (22), CC(9) tRasym(45), CBr(28), bCCN(20), CH(5) tRasym(83), CH(17) CBr(43), Rsymd(40), CC(9), CCasym(5) bCBr(75), bCCN(14) bCCNop(34), CCa (24), tRsym(22), CBr(13), CH(7) bCCNip(58), bCCa (31), bCBr(9) tRasym(56), CH(8), bCCNop(12), CCasym(9), CBr(5)
Abbreviations used: , stretching; R, ring; b, bending; d, deformation; asym, asymmetric; sym, symmetric; (, wagging; t, torsion; trig, trigonal. a Relative absorption intensities normalized with highest peak absorption equal to 1.0. b Relative Raman intensities calculated by Eq. (1) and normalized to 100. c For the notations used see Table 3.
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229 and 131 cm−1 are assigned to the individual out of plane deformation of C≡N vibration and in plane deformation of C≡N vibration, respectively [14]. 5. Conclusions Complete vibrational analysis of 4-bromo benzonitrile was performed on the basis of DFT calculations at the B3LYP/6-11+G** level of theory. The influences of nitrile, bromine in the vibrational frequencies of the title compound were discussed. The various modes of vibrations were unambiguously assigned based on the results of the TED output obtained from normal coordinate analysis. The assignment of the fundamentals is confirmed by the qualitative agreement between the calculated and observed frequencies.
Fig. 3. Comparison of observed and calculated laser Raman spectra of 4-bromo benzonitrile: (a) observed and (b) calculated with B3LYP/6-311+G**.
4.2.2. Ring vibrations Generally the C C stretching vibrations in aromatic compounds form the band in the region of 1430–1650 cm−1 . According to Socrates [14], the presence of conjugate substituents such as C O, C C, C≡N or the presence of heavy element causes a doublet formation around the region (1625–1575) cm−1 . Moreover, with bulky substituents the bands near 1600, 1580, 1490 and 1440 cm−1 may shift to lower wave numbers which is well established in the present work. A doublet band at 1563 cm−1 is assigned to C C stretching vibrations and the bands observed at lower wave numbers at 1281, 1161 and 1070 cm−1 of FTIR and 1198 cm−1 of Raman are designated to C C stretching vibrations. 4.2.3. C–Br vibrations The vibrations belonging to the bond between the ring and the Bromine atom are important as mixing of vibrations are possible due to the presence of heavy atoms [15]. C–Br bond shows lower absorption frequencies as compared to C–H bond due to the decreased force constant and increase in reduced mass. In 4-bromo benzonitrile, the C–Br stretching and out-of-plane bending modes are recorded at 545 and 278 cm−1 , respectively in IR. The FTIR band at 279 cm−1 is assigned to C–Br in-plane bending vibration. 4.2.4. C≡N vibrations The band at 2229 cm−1 in Raman spectrum is a characteristic vibration for C≡N group. The nitriles have two important deformations at 545 cm−1 of Raman band and 434 cm−1 of FTIR band are due to the out of plane aromatic ring deformation with in plane deformation of the C≡N vibration and in plane bending of the aromatic ring with the C–C≡N bending, respectively [14]. The FTIR band at
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. References [1] V. Krishnakumar, GáborKeresztury, R. Tom Sundius, Ramasamy, J. Mol. Struct. 704 (2004) 9. [2] G. Fogarasi, P. Pulay, in: J.R. Durig (Ed.), Vibrational Spectra and Structure, vol. 14, Elesevier, Amsterdam, 1985, p. 125 (Chapter 3). [3] M.J. Frisch, G.W. Trucks, H.B. Schlega, G.E. Scuseria, M.A. Robb, J.R. Cheesman, V.G. Zakrzewski, J.A. Montgomery Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, N. Roga, P. Salvador, J.J. Dannenberg, D.K. Malick, A.D. Rabuck, K. Rahavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al–Laham, C.Y. Penng, A. Nanayakkara, M. Challa–Combe, 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 11.4, Gaussian Inc., Pittsburgh, PA, 2002. [4] A.D. Becke, J. Chem. Phys. 98 (1993) 5648. [5] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1998) 785. [6] A. Berces, T. Ziegler, J. Chem. Phys. 98 (1993) 4793. [7] P. Pulay, G. Fogarasi, G. Pongor, J.E. Boggs, A. Vargha, J. Am. Chem. Soc. 105 (1983) 7037. [8] G. Fogarasi, X. Zhov, P.W. Taylor, P. Pulay, J. Am. Chem. Soc. 114 (1992) 8191. [9] (a) T. Sundius, Vib. Spectrosc. 29 (2002) 89; (b) MOLVIB: A Program for Harmonic Force Field Calculations, QCPE Program No. 807, 2002. [10] P.L. Polavarapu, J. Phys. Chem. 94 (1990) 8106. [11] T. Sundius, J. Mol. Struct. 218 (1990) 321. [12] G. Keresztury, S. Holly, J. Varga, G. Bensenyei, A.Y. Wang, J.R. Durig, Spectrochim. Acta 49A (1993) 2007. [13] G. Keresztury, B.T. Raman, Spectroscopy Theory, in: J.M. Chalmers, P.R. Griffiths (Eds.), Handbook of Vibrational Spectroscopy, vol. 1, John Wiley & Sons Ltd., 2002, p. 71. [14] G. Socrates, Infrared and Raman Characteristic Group Frequencies, third ed., John Wiley & sons, Ltd., Chichester, 2001. [15] M. Bakiler, I.V. Maslov, S. Akyiiz, J. Mol. Struct. 475 (1999) 83.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Scaled quantum chemical studies on the vibrational spectra of 4-bromo benzonitrile V. Krishnakumar a,∗ , N. Surumbarkuzhali b , S. Muthunatesan c a
Department of Physics, Periyar University, Salem 636 011, India Department of Physics, Government Polytechnic College, Krishnagiri 635001, India c Department of Physics, Government Arts College (Autonomous), Kumbakonam 612001, India b
a r t i c l e
i n f o
Article history: Received 20 December 2007 Accepted 24 June 2008 Keywords: 4-Bromo benzonitrile Density functional theory Vibrational spectra
a b s t r a c t The vibrational spectra of 4-bromo benzonitrile have been reported. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6-311+G basis set combination and were scaled using various scale factors which yielded a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound which showed excellent agreement with the observed spectra. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Benzonitrile, derived mainly from benzoic acid reaction with lead thiocyanate by heating, is a clear liquid; boils at 191 ◦ C. It reacts violently with strong acids to produce toxic hydrogen cyanide. It decomposes on heating, producing very toxic fumes, hydrogen cyanide, nitrous oxides [1]. Benzonitrile is used as a solvent and chemical intermediate for the synthesis of pharmaceuticals, dyestuffs and rubber chemicals through the reactions of alkylation, condensation, esterification, hydrolysis, halogenation or nitration. Benzonitrile and its derivatives are used in the manufacture of lacquers, polymers and anhydrous metallic salts as well as intermediates for pharmaceuticals, agrochemicals, and other organic chemicals. Due to greater pharmaceutical importance, 4-bromo benzonitrile has been taken for the present study. The complete vibrational analysis of 4-bromo benzonitrile was performed by combining the experimental and theoretical information using Pulay’s density functional theory (DFT)-based scaled quantum chemical approach [2]. 2. Experimental details The fine sample of 4-bromo benzonitrile was obtained from Lancaster chemical company, UK, and used as such for the spectral measurements. The FTIR spectrum of the title compound
∗ Corresponding author. E-mail address: vkrishna [email protected] (V. Krishnakumar). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.06.037
was recorded using PerkinElmer spectrum RX1 spectrophotometer equipped with He–Ne laser source in the region 100–4000 cm−1 using KBr and polyethylene pellets. The FT-Raman spectra were recorded on Bruker IFS-66V model interferometer equipped with an FRA-106 FT-Raman accessory in the 3500–100 cm−1 Stokes region using the 1064-nm line of Nd: YAG laser for excitation operating at 200 mW power. The reported wave numbers are believed to be accurate within ±1 cm−1 . 3. Computational details The quantum chemical calculations were performed by applying DFT method using the Gaussian 98W program [3] using the Becke 3-Lee-Yang-Parr (B3LYP) functional [4] supplemented with the standard 6-311+G** basis set [5,6]. The Cartesian representation of the theoretical force constants has been computed at the fully optimized geometry by assuming CS point group symmetry. Scaling of the force field was performed according to the SQM procedure [7,8] using selective scaling in the natural internal coordinate representation [2,8]. Transformations of the force field and the subsequent normal coordinate analysis including the least squares refinement of the scaling factors, calculation of total energy distribution (TED) and prediction of IR and Raman Intensities were done on a PC with the MOLVIB program written by Sundius [9,10]. The TED elements provide a measure of each internal coordinate’s contributions to the normal coordinate. For the plots of simulated IR and Raman spectra, pure Lorentzian band shapes were used with a bandwidth of 10 cm−1 . The prediction of Raman intensities was carried out by following the
V. Krishnakumar et al. / Spectrochimica Acta Part A 71 (2009) 1810–1813
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Table 1 Optimized geometrical parameters of 4-bromo benzonitrile Bond length
Value (Å)
Bond angle
Value (◦ )
C1–C2 C2–C3 C3–C4 C4–C5 C5–C6 C1–C7 C2–H8 C3–H9 C4–Br10 C5–H11 C6–H12 C1–H13
1.4047 1.3912 1.3952 1.3952 1.3913 1.4336 1.0845 1.0837 1.9054 1.0837 1.0845 2.5969
C1–C2–C3 C2–C3–C4 C3–C4–C5 C4–C5–C6 C2–C1–C7 C3–C2–H8 C4–C3–H9 C5–C4–Br10 C6–C5–H11 C1–C6–H12 C2–C1–N13 C6–C5–C4–Br10 C3–C2–C1–N13
120.1313 119.2682 121.3755 119.2674 120.0864 120.1224 120.1964 119.311 120.539 120.539 120.539 180 180
For numbering of atoms refer Fig. 1. Fig. 1. Molecular model of 4-bromo benzonitrile along with numbering of atom.
4.2. Vibrational analysis of and theoretical prediction of spectra procedure outlined below. The Raman activities (Si ) calculated by the Gaussian 98W program and adjusted during the scaling procedure with MOLVIB were converted to relative Raman intensities (Ii ) using the following relationship derived from the basic theory of Raman scattering [11–13]: Ii =
f (0 − i )4 Si i [1 − exp(−hci /KT )]
(1)
where 0 is the exciting frequency (cm−1 units); i the vibrational wave number of the normal mode; h, c and k are the universal constants, and f is the suitably chosen common normalization factor for all the peak intensities.
The 33 normal modes of 4-bromo benzonitrile are distributed amongst the symmetry species as vib = 23A (in-plane) + 10A (out-of-plane) In agreement with Cs symmetry, all the vibrations are active both in Raman scattering and infrared absorption. The detailed vibrational assignments of fundamental modes of 4-bromo benzonitrile along with the calculated IR, Raman intensities and normal mode descriptions were reported in Table 4. For visual comparison, the observed and simulated FTIR and laser Raman spectra were presented in Figs. 2 and 3, respectively. Root mean square (RMS) values of frequencies were obtained using the following expression:
n 1 exp 2 RMS = (icalcu − i )
4. Results and discussion 4.1. Molecular geometry
n−1
The molecular structure of the 4-bromo benzonitrile having Cs point group of symmetry is shown in Fig. 1. The global minimum energy was obtained by the DFT structure optimization and was calculated as −2895.60183060 hartrees. The most optimized structural parameters were also calculated and they were depicted in Table 1.
(2)
i
The RMS error of frequencies (unscaled/B3LYP/6-311+G**) obtained for 4-bromo benzonitrile was found to be 94.62 cm−1 . In order to reproduce the observed frequencies, refinement of scaling factors was applied and optimized via least square refinement algorithm which resulted a RMS deviation of 7.27 cm−1 .
Table 2 Definitions of internal coordinates of 4-bromo benzonitrile No.
Symbol
Type
Definition
Stretching 1–4 5 6 7 8–13
ri Ri Qi qi Ti
C–H C–C (aromatic) C–Br C–N C–C (ring)
C2–H8, C3–H9, C4–H11, C5–H12 C1–C7 C4–Br10 C1–N13 C1–C2, C2–C3, C3–C4, C4–C5, C5–C6, C6–C1
Bending 14–21 22–27 28–29 30–31 32–33
ˇi i i ˛i i
C–C–H C–C–C (ring) C–C–C (aromatic) C–C–Br C–C–N
C3–C2–H8, C1–C2–H8, C4–C3–H9, C2–C3–H9, C6–C5–H11, C4–C5–H15, C1–C6–H12, C5–C6–H12 C1–C2–C3, C2–C3–C4, C3–C4–C5, C4–C5–C6, C5–C6–C1, C6–C1–C2 C7–C1–C2, C7–C1–C6 C5–C4–Br10, C3–C4–Br10 C2–C1–N13, C6–C1–N13
C–H C–Ca C–Br C–N ring
H8–C2–C3–C1, H9–C3–C4–C2, H11–C5–C6–C4, H12–C6–C1–C5 C7–C1–C2–C6 Br10–C4–C5–C3 N13–C1–C2–C6 C1–C2–C3–C4, C2–C3–C4–C5, C3–C4–C5–C6, C4–C5–C6–C1, C5–C6–C1–C2, C6–C1–C2–C3
Out-of-plane bending 34–37 ωi 38 ϕi 39 i 40 i 41–46
i For numbering of atoms refer Fig. 1.
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Table 3 Definition of local symmetry coordinates for 4-bromo benzonitrile No. (i)
Symbola
Definitionb
1–4 5 6 7 8–13 14–17
CH CC (nitrile) C Br CN CC (Ring) bCH
18–20
Rtrigd Rsymd R asymd bCC bCBr bCN CH CC CBr CN tRsym tRasym tRtrigd
r1 , r2 , r3 , r4 R5 Q6 q7 T8 , T9 , T10 , T11 √, T12 , T13 √ (ˇ14 −√ˇ15 )/ 2, (ˇ16 −√ˇ17 )/ 2, (ˇ18 − ˇ19 )/ 2, (ˇ20 − ˇ21 )/ 2 √ (22 − 23 + 22 − 24 + 26 − 27 )/ 6 √ (−22 − 23 + 224 − 25 + 26 − 227 )/ 12 ( 22 − 23 +√25 − 26 )/2 (28 − 29 )/ √2 (˛30 − ˛31 )/√ 2 (32 − 33 )/ 2 ω34 , ω35 , ω36 , ω37 ϕ38 39 40 ( 41 − 42 + 44 − 45 )/2 √ (− 41 + 2 42 − 43 − 44 + 2 45 − √ 46 )/ 12 ( 41 − 42 + 43 − 44 + 45 − 46 )/ 6
21 22 23 24–27 28 29 30 30–33
a b
These symbol are used for description of normal modes by TED in Table 4. The internal coordinates used here are defined in Table 2.
4.2.1. C–H vibrations The aromatic organic compounds always have C–H stretching vibrations in the region 3000–3100 cm−1 which is the character-
Fig. 2. Comparison of observed and calculated FTIR 4-bromo benzonitrile: (a) observed and (b) calculated with B3LYP/6-311+G**.
istic region for the ready identification of C–H vibrations. These vibrations are not found to be affected due to the nature and position of the substituents. The FTIR band at 3086, 3064 and 3047 cm−1 and Raman band at 3076 cm−1 are assigned to C–H stretching vibrations. The C–H bending vibrations are usually occurring in the region 1465–1281 cm−1 [14]. As the C–C stretching vibrations are shifting to the lower wave numbers, C–H bending vibrations are dominating in this region. The assignments of in plane and out of plane C–H bending vibrations are as shown in Table 4.
Table 4 Observed and B3LYP/6–311+G** level calculated vibrational frequencies (cm−1 ) of 4-bromo benzonitrile No.
1 2 3 4 5 6 7 8 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
Symmetry species
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
Observed frequency (cm−1 )
Calculated frequency (cm−1 ) with B3LYP/6-311+G** force field
IR
Unscaled
Scaled
IRa (Ai )
Ramanb (Ii )
3230 3229 3214 3213 2350 1644 1608 1526 1436 1332 1329 1226 1205 1135 1090 1028 986 986 852 850 785 732 652 565 557 546 444 417 274 263 229 134 80
3076 3075 3061 3060 2229 1622 1574 1563 1462 1389 1277 1240 1198 1149 1072 1010 977 970 858 836 731 731 655 563 547 545 434 406 278 264 232 128 80
0.008 1.349 0.7 0.959 32.033 31.321 0.330 54.697 10.659 0.388 2.135 5.197 1.751 1.475 43.167 30.805 0.000 0.001 37.197 0.000 6.055 0.870 0.065 20.677 0.014 9.208 0.060 0.000 1.006 0.153 2.887 6.698 4.163
219.77 3.539 89.938 19.384 536.156 166.249 1.125 0.865 0.137 1.158 0.001 24.978 62.151 0.048 33.803 3.473 2.894 0.001 0.894 5.387 18.968 0.315 3.640 2.314 2.657 0.422 4.153 0.005 5.830 2.099 0.005 2.618 0.930
3086 – 3064 3047 1608 1563 1563 1465 1387 1281 1256
Raman 3076 – – 2229 – – –
1198 1161 1070 1015 986 964 868 825 774 722 653 565 545 544 434 417 279 263 229 131 86
TED (%) among type of internal coordinatesc
CH(99) CH(99) CH(99) CH(99) CN(87), CCasym(12) CC(53), bCH(35), Rtrigd(9) CC(61), bCH(26), Rsym(9) bCH(71), CC(26) bCH(60), CC(34) bCH(71), CC(21) CC(94) bCH(62), CC(36) CCasym(41), CC(26), bCH(10), Rasymd(17) CC(52), bCH(40) CC(66), CBr(22), bCH(8) Rsymd(60), Rtrigd(9), CC(22), CBr(6) CH(75), tRsymd(20) CH(92), tRsymd(8) CH(70), tRsymd(12), CCa (10), CBr(6) CH (100) Raymd(29), Rtrigd(12), CC(28), CCa (16), CBr(9) tRsym(66), CCa (16), CBr(13) Rasymd(61), bCCa (17), CC(15) tRasym(31) Rsymd(38), bCCaym(35), bCCN(18), CC(6) CBr(34), Rsymd(32), CCa (22), CC(9) tRasym(45), CBr(28), bCCN(20), CH(5) tRasym(83), CH(17) CBr(43), Rsymd(40), CC(9), CCasym(5) bCBr(75), bCCN(14) bCCNop(34), CCa (24), tRsym(22), CBr(13), CH(7) bCCNip(58), bCCa (31), bCBr(9) tRasym(56), CH(8), bCCNop(12), CCasym(9), CBr(5)
Abbreviations used: , stretching; R, ring; b, bending; d, deformation; asym, asymmetric; sym, symmetric; (, wagging; t, torsion; trig, trigonal. a Relative absorption intensities normalized with highest peak absorption equal to 1.0. b Relative Raman intensities calculated by Eq. (1) and normalized to 100. c For the notations used see Table 3.
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229 and 131 cm−1 are assigned to the individual out of plane deformation of C≡N vibration and in plane deformation of C≡N vibration, respectively [14]. 5. Conclusions Complete vibrational analysis of 4-bromo benzonitrile was performed on the basis of DFT calculations at the B3LYP/6-11+G** level of theory. The influences of nitrile, bromine in the vibrational frequencies of the title compound were discussed. The various modes of vibrations were unambiguously assigned based on the results of the TED output obtained from normal coordinate analysis. The assignment of the fundamentals is confirmed by the qualitative agreement between the calculated and observed frequencies.
Fig. 3. Comparison of observed and calculated laser Raman spectra of 4-bromo benzonitrile: (a) observed and (b) calculated with B3LYP/6-311+G**.
4.2.2. Ring vibrations Generally the C C stretching vibrations in aromatic compounds form the band in the region of 1430–1650 cm−1 . According to Socrates [14], the presence of conjugate substituents such as C O, C C, C≡N or the presence of heavy element causes a doublet formation around the region (1625–1575) cm−1 . Moreover, with bulky substituents the bands near 1600, 1580, 1490 and 1440 cm−1 may shift to lower wave numbers which is well established in the present work. A doublet band at 1563 cm−1 is assigned to C C stretching vibrations and the bands observed at lower wave numbers at 1281, 1161 and 1070 cm−1 of FTIR and 1198 cm−1 of Raman are designated to C C stretching vibrations. 4.2.3. C–Br vibrations The vibrations belonging to the bond between the ring and the Bromine atom are important as mixing of vibrations are possible due to the presence of heavy atoms [15]. C–Br bond shows lower absorption frequencies as compared to C–H bond due to the decreased force constant and increase in reduced mass. In 4-bromo benzonitrile, the C–Br stretching and out-of-plane bending modes are recorded at 545 and 278 cm−1 , respectively in IR. The FTIR band at 279 cm−1 is assigned to C–Br in-plane bending vibration. 4.2.4. C≡N vibrations The band at 2229 cm−1 in Raman spectrum is a characteristic vibration for C≡N group. The nitriles have two important deformations at 545 cm−1 of Raman band and 434 cm−1 of FTIR band are due to the out of plane aromatic ring deformation with in plane deformation of the C≡N vibration and in plane bending of the aromatic ring with the C–C≡N bending, respectively [14]. The FTIR band at
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. References [1] V. Krishnakumar, GáborKeresztury, R. Tom Sundius, Ramasamy, J. Mol. Struct. 704 (2004) 9. [2] G. Fogarasi, P. Pulay, in: J.R. Durig (Ed.), Vibrational Spectra and Structure, vol. 14, Elesevier, Amsterdam, 1985, p. 125 (Chapter 3). [3] M.J. Frisch, G.W. Trucks, H.B. Schlega, G.E. Scuseria, M.A. Robb, J.R. Cheesman, V.G. Zakrzewski, J.A. Montgomery Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, N. Roga, P. Salvador, J.J. Dannenberg, D.K. Malick, A.D. Rabuck, K. Rahavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al–Laham, C.Y. Penng, A. Nanayakkara, M. Challa–Combe, 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 11.4, Gaussian Inc., Pittsburgh, PA, 2002. [4] A.D. Becke, J. Chem. Phys. 98 (1993) 5648. [5] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1998) 785. [6] A. Berces, T. Ziegler, J. Chem. Phys. 98 (1993) 4793. [7] P. Pulay, G. Fogarasi, G. Pongor, J.E. Boggs, A. Vargha, J. Am. Chem. Soc. 105 (1983) 7037. [8] G. Fogarasi, X. Zhov, P.W. Taylor, P. Pulay, J. Am. Chem. Soc. 114 (1992) 8191. [9] (a) T. Sundius, Vib. Spectrosc. 29 (2002) 89; (b) MOLVIB: A Program for Harmonic Force Field Calculations, QCPE Program No. 807, 2002. [10] P.L. Polavarapu, J. Phys. Chem. 94 (1990) 8106. [11] T. Sundius, J. Mol. Struct. 218 (1990) 321. [12] G. Keresztury, S. Holly, J. Varga, G. Bensenyei, A.Y. Wang, J.R. Durig, Spectrochim. Acta 49A (1993) 2007. [13] G. Keresztury, B.T. Raman, Spectroscopy Theory, in: J.M. Chalmers, P.R. Griffiths (Eds.), Handbook of Vibrational Spectroscopy, vol. 1, John Wiley & Sons Ltd., 2002, p. 71. [14] G. Socrates, Infrared and Raman Characteristic Group Frequencies, third ed., John Wiley & sons, Ltd., Chichester, 2001. [15] M. Bakiler, I.V. Maslov, S. Akyiiz, J. Mol. Struct. 475 (1999) 83.