Study of vibrational spectra of 4-methyl-3-nitrobenzaldehyde

Transcription

1 Indian Journal of Pure & Applied Physics Vol. 44, September 2006, pp Study of vibrational spectra of 4-methyl-3-nitrobenzaldehyde B S Yadav, S K Tyagi* & Seema** Molecular Spectroscopy and Biophysics Laboratory, D N (PG) College, Meerut Department. of Physics, C S S S (P G ) College, Machhra (Meerut) U P Department. of Chemistry, J V College, Baraut, U P sktyagi12@rediffmail.com Received 13 September 2005; revised 22 December 2005; accepted 6 July 2006 The vibrational (infrared and Raman) spectra of 4-methyl-3-nitrobenzaldehyde have been reported. The assignments of fundamentals are proposed and discussed by assuming the molecule under C S point group symmetry. Keywords: Infrared and Raman specroscopy, vibrational frequencies, methyl nitro benzaldehyde IPC Code: G01J3/28 1 Introduction Benzaldehyde is the simplest aromatic aldehyde and the substitution of a functional group in benzaldehyde changes the spectra markedly. The vibrational spectra of benzaldehyde and its derivatives have been extensively investigated by many earlier researchers 1-7. In the present study, vibrational, spectra of 4-methyl-3-nitrobenzaldehyde have been discussed. 2 Experimental Details The compound 4-methyl-3-nitrobenzaldehyde (hereafter referred as 4,3-MNB) is solid (m p 46 C) at room temperature and was obtained in pure form from M/s Aldrich Chemical Co, USA. Its purity was confirmed by elemental analysis and by determining the melting point. The IR and laser Raman spectra have been recorded at room temperature. The infrared spectra of the compound 4,3-MNB were recorded in KBr pellets and nujol mull solvent in the region cm -1 on a Perkin-Elmer 983 spectrometer equipped with a computer datamate. A photoconductivity cell is used for detection of IR. The laser Raman spectra of 4,3-MNB was recorded in the region cm -1 on a Spex model 1403 spectrometer equipped with double monochrometer and computer datamate. The sample was placed in a quartz cell and to excite this, the 4880 Å line of an Ar + laser was used. The laser power on the sample was in the range mw. The Raman frequencies are accurate within ± 2 cm -1 and the resolution of the spectrometer under the present experimental condition was of the order of 2 cm -1. The time constant was kept 0.25 sec and scanning speed was 100 cm -1 /min. 3 Results and Discussion The molecule 4,3-MNB is assumed to belong to C S point group symmetry. The molecular structure of the compound 4,3-MNB is shown in Fig. 1. The laser Raman and IR spectra of KBr pellets and nujol mull are shown in Figs 2-4, respectively. The observed fundamental frequencies and their proposed assignments are given in Table 1. NO2 CHO CH3 Fig. 1 Molecular structure of 4,3-MNB 3.1 Vibrational spectra ring vibrations The molecule 4,3-MNB is a tri-substituted benzene and so three C-H valence oscillations are expected in

2 YADAV et al.: VIBRATIONAL SPECTRA OF 4-METHYL-3-NITROBENZALDEHYDE 645 Fig. 2 IR absorption spectrum of 4, 3-MNB in nujolmull the region cm -1. Thus, the frequencies observed at 3003 cm -1 (KBr), 3089 (nujol)/3091 cm -1 (Raman) and 3102 cm -1 (KBr) have been assigned to C-H stretching (aromatic). In tri-substituted benzene derivatives, three modes of vibrations remain almost unchanged and are called (C-H) in-plane bending and out-of-plane bending vibrations. The C-H in-plane and C-H out-of-plane modes lie in the region cm -1 and cm -1, respectively 9. Hence, the band at 1022 cm -1 (KBr)/1027 cm -1 (nujol) with the counter part of Raman band at 1030 cm -1 have been assigned to (C- H) in-plane bending while the frequencies at 900 cm -1 (KBr)/904 cm -1 (nujol) have been assigned to (C-H) out-of-plane bending modes. The appearance of a group of six bands in the region cm -1 represent (C-C) stretching modes. Exccept for ring breathing vibrations of benzene, all the frequencies are known to remain practically unaffected by substitution. It has been pointed out by several researchers that the reduced symmtry C S, C-C breathing and C-C-C trigonal bending vibrations give rise to the combined modified modes. As a result, one of the modified modes is reduced to about 800 cm -1 while the other keeps itself around 1000 cm -1 in substituted benzene 10,11. These modes in the title compound are in agreement with the literature available for substituted benzaldehydes. The in-plane (C-C-C) bending vibrations of benzene lead to three such vibrations in substituted benzenes. The frequencies observed in the spectrum of the compound are presented in Table 1. Similarly C-C-C out-of-plane bending vibrations are also possible which have also been observed and presented in Table C-X vibrations Goel and Agarwal 12 have assigned the C-CH 3 stretching mode at 1185, 1184 and 1170 cm -1 in 2,6- diamino toluene, 2,4 diamino toluene and 3,4-diamino toluene, respectively. Hence, the band observed at 1169 cm -1 (nujol) with the counter part of Raman band at 1176 cm -1 have been assigned to C-CH 3 stretching mode which is in good agreement with the literature values 13. The very strong band at 1214 cm -1 with the counter part of Raman band at 1226 cm -1

3 646 INDIAN J PURE & APPL PHYS, VOL. 44, SEPTEMBER 2006 Fig. 3 Laser Raman spectrum of 4, 3-MNB Fig. 4 IR absorption spectrum of 4, 3-MNB in KBr pellets

4 YADAV et al.: VIBRATIONAL SPECTRA OF 4-METHYL-3-NITROBENZALDEHYDE 647 have been assigned to C-CHO stretching mode which find support from Varsanyi 14. The C-NO 2 stretching mode is expected around 1100 cm -1. In the present study, the band observed at 1070 (KBr)/1077 cm -1 (nujol) with the counter part of Raman band at 1080 cm -1 is assigned to C-NO 2 mode which finds support from the value assigned by Mathew et al 15. The bands observed at 328 cm -1 is assigned to C- NO 2 in-plane bending and at 160 cm -1 in Raman spectrum may be assigned to C-NO 2 out-of-plane bending, respectively which is in good agreement with the Mathew et al 15. Singh and Singh 16 have assigned in-plane bending for CH 3 group at 354 and 376 cm -1 for 2,4-difluoro toluene and 2,5-difloro toluene, respectively. Hence, the frequency at 371 cm -1 has been assigned to inplane bending for C-CH 3 while the frequency at 328 cm -1 has been assigned to CH 3 out-of-plane bending mode which agree with the literature values Group vibration NO 2 antisymmetric and symmetric stretching have been assigned on account of their characteristic magnitudes. The mode ν as (NO 2 ) has higher frequency compared to the ν s (NO 2 ) mode. In the present investigation, the IR bands observed at 1560 cm -1 (KBr)/1562 cm -1 nujol have been assigned to NO 2 asymmetric stretching mode which find support from Raman value obtained at 1553 cm -1. The IR bands at 1345 cm -1 (KBr)/1352 cm -1 (nujol) represent NO 2 symmetric stretching mode. These also find support from Raman value at 1355 cm -1. The frequencies at 732 cm -1 (nujol)/754 cm -1 (KBr) have been assigned to NO 2 wagging mode. The strong band observed at 853 cm -1 has been assigned to NO 2 deformation mode. The band observed at 545 cm -1 has been assigned to NO 2 rocking vibration. These assignments are in good agreement with the earlier researchers The NO 2 torsion mode is observed in the range cm -1, hence the Raman band at 102 cm -1 has been assigned to this mode. The C-H stretching and C-H deformations due to methyl group have been assigned in their respective region in Table 1. The CH 3 rocking mode has been identified at 1070 cm -1 (KBr)/1077 cm -1 (nujol). These assignments are in good agreement with the values reported in the literature 20,21. In the methyl group, there are three CH stretching vibrations, one being symmetric and the other two asymmetric. The frequencies of asymmetric vibrations are higher then that of symmetric. In the Table 1 Assignment of vibrational frequencies of 4,3-MNB (All values are in cm -1 ) Raman KBr IR Nujolmull Assignments 56vs CHO torsion 102sb NO 2 torsion 119w H.B. 160ms γ(c-no 2 ) 192w CH 3 torsion 328w β(c-no 2 ), γ(c-ch 3 ) 371w β(c-oh), β(c-ch 3 ) 407vw γ(c-c), β(c-cho) 432w γ(c-c) 472w β(c-c) 488m γ(c-c-c) 545m NO 2 rocking 586s β(c-ch 3 ) 607m β(c-c-c) 652s 648s β(c-c) 691m γ(c-c) 719vw 712m 715s ν(c-c) ring breathing 754vw 732m γ(c=o), NO 2 wagging 840vs 840m β(c=o) 853s NO 2 def 900m 904m γ(c-h) 930vw 918w 926s (C-C-C) triogonal bending 1030m 1022m 1027w β(c-h) 1080vw 1070w 1077w CH 3 rocking, ν(c-no 2 ) 1176w 1169s ν(c-ch 3 ) 1226vs 1214vs ν(c-cho) 1306s ν(c-c), b 2 u(1310) kekule 1355vs 1345s 1352vs NO 2 symm. stre. 1383w 1383m β(c-h) aldehydic 1457m 1457w ν(c-c), e 1u (1485) 1522s 1530vs ν(c-c), e 1u (1485) 1553m 1560w 1562m NO 2 asy. str. 1590w ν(c-c), e 2g (1595) 1640vs 1618s 1627vvs ν(c-c), e 2g (1595) 1708vs 1708vs ν(c=o), CHO Group 2752m ν(c-h) symm.(aldehydic) 2843wb 2850m ν(c-h) symm. CH 3 group 2936m ν(c-h) asymm. 2965m ν(c-h) asymm. 3003w ν(c-h) aromatic 3091m 3089w ν(c-h) aromatic 3102w ν(c-h) aromatic where ν = stretching, β=in-plane bending, γ=out-of-plane bending, w=weak, m=medium, s=strong, vs=very strong, vw=very weak, symm=symmetric, asym=asymmetic, H.B.=Hydrogen bonding, def=deformation. present case, the frequencies 2936 cm -1 (KBr) and 2965 cm -1 Raman have been assigned to asymmetric stretching while the frequencies 2843 cm -1 (KBr)/2850 cm -1 nujol have been assigned to symmetric stretching.

5 648 INDIAN J PURE & APPL PHYS, VOL. 44, SEPTEMBER 2006 The aldehyde group gives rise to six vibrations namely C=O stretching, C=O in-plane bending, C=O out-of-plane bending C-H stretching, C-H in-plane bending and C-H out-of-plane bending vibrations. The C=O stretching is the prominent vibration of the aldehydic group which is observed with strong intensity in CHO group. The strong band at 1708 cm -1 has been assigned to C=O stretching vibration which lies in the region reported by earlier researchers 23,24. The C=O in-plane bending vibration is observed in the region cm -1 in many of the substituted benzaldehydes and the strong band at 840 cm -1 has been assigned to this vibration. The C-H stretching vibration is expected in the region cm -1. The band observed at 2752 cm -1 is assigned to this mode. The band observed at 1383 cm -1 has been assigned to C-H in-plane bending vibration. Acknowledgement The authors are thankful to RSIC, Indian Institute of Technology, Mumbai, for recording the laser Raman and IR spectra. References 1 Gupta S P, Gupta C, Sharma S & Goel R K, Indian J Pure & Appl Phys, 24 (1986) Venkoji, Indian J Pure & Appl Phys, 24 (1986) Gupta S P, Gupta C, Seema & Goel R K, Indian J Phys, 62B (4), (1988) Katti N R, Aralakkanvar M K, Jeergal P R, Rao Rekha & Shashidhar M A, Indian J Phys 66B, 2 (1992) Katti N R, Aralakkanvar M K, Jeergal P K, Kalkati G B & Shashidhar M A, Indian J Phys 66B, 3 (1992) Singh D N, Singh I D & Yadav R A, Indian J Phys 76B (3), (2002) Singh D N, Singh I D & Yadav R A, Indian J Phys, 76B (1) (2002) Krishan Kumar V & Xavier R John, Indian J Pure & Appl Phys, 41 (2003) Yadav B S, Singh V, Yadav M K & Chaudhary Sanjeev, Indian J Pure & Appl Phys, 35 (1997) Tripathi R S, Indian J Pure & Appl Phys, 11 (1973) Sharma S N & Diwedi C P D, Indian J Pure & Appl Phys, 13 (1975) Goel R K & Agarwal M L, Indian J Pure & Appl Phys, 21 (1983) Goel R K, Sharma S D, Kansal K P & Sharma S N, Indian J Pure & Appl Phys, 18 (1980) Varsanyi G, Assignments for vibrational spectra of seven hundred benzene derivative vol. I & II (Adm. Hilger London) Mathew S, Ahmed S & Verma P K, Indian J Pure & Appl Phys, 31 (1993) Singh R P & Singh R N, Indian J Pure & Appl Phys, 26 (1988) Goel R K, Spectrochim Acta 40A, 8 (1984) Mooney E F, Spectrachimacta Part A, 20 (1964) Yadav B S, Kumar V, Singh V, Yadav M K & Chand S, Indian J Phys, 72B (1998) Gupta S P, Sharma S D, Jetley U K, Yadav B S & Gupta Y K, Oriental J Chem 6, 2 (1990) Green J H S, Harrison D J & Kyanston W, Spectrochim Acta, 27A, (1971) Goel R K & Agarwal M L, J Chem Phys, 79 (1982) Sanyal N K, Goel R K & Agarwal M L, Indian J Pure & Appl Phys, 19 (1981) Upadhyay A P & Upadhyay K N, Indian J Phys Part-B, 55 (1981) 232.