FTIR, FT-Raman spectral analysis and normal coordinate calculations of 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone

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1 Indian Journal of Pure & Applied Physics Vol. 42, May 2004, pp FTIR, FT-Raman spectral analysis and normal coordinate calculations of 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone V Krishnakumar & V Balachandran * Post-graduate Department of Applied Physics, Nehru Memorial College, Puthanampatti , Tiruchirappalli, Tamil Nadu *Department of Physics, Thanthai Hans Roever College, Perambalur , Tamil Nadu Received 22 April 2003, revised 21 November 2003, accepted 9 January 2004 The normal coordinate analysis of 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone has been carried out by using a modified Urey-Bradley Force Field. The calculated frequencies were obtained by considering the interaction between nonneighboring stretching and bending vibrations and by introducing an appropriate set of internal coordinates in the course of calculations. All the functional modes of vibrations are assigned and discussed in detail. [Key words: Normal coordinate analysis, Vibrational spectra, Hydroxy methoxybenzaldehyde thiosemicarbozone, Potential energy] IPC Code: G 01J 3/44 1 Introduction Thiosemicarbozones have been more extensively studied on account of their intrinsic interest as compounds of great biological, antibacterial, germicidal and antifungal activity 1-5. The vibrational analysis of the title compound has been studied and assigned on the basis of group frequencies approached by B S Yadav et al. 6. However, in the absence of normal coordinate calculations, the assignments of vibrational frequencies were only tentative. The complete vibrational analysis of the polyatomic molecules is possible only when both the IR and Raman spectral data are available. Hence, in the present study the Raman spectral data of the title compound was experimentally obtained and used in the normal coordinate analysis calculations along with the IR data already reported in the literature. 2 Theory and Experimentation 2.1 Molecular symmetry The molecular structure of the title compound is shown in Fig. 1. From the structural point of view the molecule belongs to C s point group symmetry. The 72 fundamental modes of vibrations are distributed to 49 in-plane vibrations (a I ) and 23 out-of-plane vibrations (a II ). Fig. 1 Molecular structure ofg 2-hydroxy-3- methoxybenzaldehyde thiosemicarbozone 2.2 Recording of the spectrum Pure chemical of 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone was obtained from Lancaster Chemical Company, UK and used as such without any further purification. The FT-Raman spectrum was recorded on BRUKER IFS66V model spectrophotometer with FRA-106 FT-Raman accessories in the region cm -1. Nd : YAG laser operating at 200 mw power with 1064 nm excitation was used as source. The observed FT- Raman spectrum of the title compound is shown in Fig. 2.

2 314 INDIAN J PURE & APPL PHYS, VOL 42, MAY 2004 Fig. 2 FT Raman spectrum of 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone 2.3 Normal coordinate analysis Normal coordinate analysis is a powerful tool for understanding the vibrational properties of a polyatomic molecule. The initial step in such a calculation is to evaluate a complete set of quadratic force constants for the molecule. There are two general procedures to evaluate the potential energy constants. One of them is to build an empirical force field by transferring the force constants from related systems; the second is to calculate them from analytical or numerical derivatives of the molecular energy obtained by using a semiempirical or ab initio Hamiltonian. In this study, an empirical force field calculation based on Urey-Bradley Force Field (UBFF) using Wilson s FG matrix mechanism 7 has been carried out and on the basis of this analysis the previous tentative assignments proposed for this molecule is reviewed. CART, GMAT and FPERT programs developed by J H Schachtschneider 8 are used in this study for evaluating the potential energy constants with suitable modifications. The redundant symmetry coordinates were eliminated during normalization by GMAT program. The initial values of the force constants were transferred from the related molecules and refined in accordance with the position of bands in the recorded spectrum. 3 Results and Discussion 3.1 Force constants The potential energy constants obtained in this study are presented in Table 1. The objective of this investigation is to find out the stretching, bending and interaction force constants corresponding to each constituent and its position in the ring. The value of the force constants f d and f R between carbon and nitrogen, carbon and sulphur are found to be and m dyne Å -1 respectively. The higher value of the potential energy constants also confirms the double bond characteristics between the respective atoms. In the process of refinement of force constants the interaction force constants are slowly introduced in order to minimize the differences between the observed and calculated frequencies. A zero order vibrational analysis was also made to check the reliability of force constants obtained in this study. 3.2 Vibrational analysis The vibrational spectral data of the title compound was assigned with the help of normal coordinate calculations. The observed and calculated frequencies along with the percentage of potential energy distribution are given in Table 2. The

3 KRISHNAKUMAR & BALACHANDRAN: NORMAL COORDINATE ANALYSIS 315 Table 1 Final set of force constants of a 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone [in the units of m.dyne Å -1 ; m.dyne rad 1 ; m.dyne Å -1 rad -2 ] Type of constants Parameters Coordinates Value Diagonal constants Stretching f p C H f q C C f r C O f t C O f d C = N f U N N f D N H f R C = S f Q C N f S O H Bending f α CCC f β CCH f γ CCO f ψ COC f φ CCN f δ HCN f ρ NCN f θ NNH f η NCS f ω CNH f μ CNN f σ COH Interaction constants Stretch stretch f pq CH CC f qq CC CC f qr CC CO f ts CO OH f rr CO CO f qt CC CO f pd CH CN f UD NN NH f DQ NH NC f RQ CS CN Contd Table 1 Final set of force constants of a 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone [in the units of m.dyne Å -1 ; m.dyne rad 1 ; m.dyne Å -1 rad -2 ] Contd. Type of constants Parameters Coordinates Value Stretch bend f pα CH CCC f qα CC CCC f rα CO CCC f tα CO CCC f qβ CC CCH f rβ CO CCH f rγ CO CCO f qφ CC CCN f Uδ NN NCH f Uρ NN NCN f Dμ NH NNC f Dη NH NCS f Dρ NH NCN f dθ CN NNH f qσ CC COH Bend bend f αα CCC CCC f αβ CCC CCH f αγ CCC CCO f δθ NCH NNH f αψ CCC COC f γψ CCO COC f ψβ COC CCH f γσ CCO COH f ασ CCC COH f μρ CNN NCN calculated fundamental frequencies agree well with the observed frequencies. 3.3 O-H Vibrations The precise position of O-H band dependent on the strength of hydrogen bond. The O-H stretching appears at cm -1 in the intramolecular hydrogen bonded systems. The observed peaks in this region will be sharp and strong 9. In this study the title compound showed a very strong absorption peak at 3480 cm -1 which is due to the O-H stretching vibration. The in-plane and out-of-plane bending vibrations of the hydroxyl group are also identified

4 316 INDIAN J PURE & APPL PHYS, VOL 42, MAY 2004 Table 2 Vibrational assignments of 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone along with calculated frequencies (in cm -1 ) and potential energy distribution Species FTIR* frequency and FT-Raman frequency and Calculated frequency Assignments (%) PED a I 3480 vs O-H stretching (98) a I ms 3371 N-H stretching (96) a I 3360 s N-H stretching (97) a I 3347 vs N-H stretching (93) a I 3165 vs 3160 vs 3154 C-H stretching (99) a I 3125 w 3110 w 3117 C-H stretching (98) a I m 3068 C-H stretching (99) a I 3032 vs C-H stretching (98) a I 3020 w C-H stretching (97) m - - CH 3 asymmetric stretching a I 2925 m 2926 ms 2915 C-H stretching (99) a I 2870 m 2863 m 2852 C-H stretching (98) s - - CH 3 asymmetric stretching vw - - NH 2 scissoring a I 1655 s 1659 w 1649 C=N stretching (88) a I 1648 m 1654 vs 1645 C-N stretching (87) a I 1600 vs 1600 s 1588 C-C stretching (99) a I 1590 m 1578 C-C stretching (98) w 1576 C-C stretching (99) a I 1544 vs 1544 s 1540 C-N stretching (83) a I m 1536 C-C stretching (96) vs - - CH 3 asymmetric deformation a I 1440 vs N-C=S symmetric stretching (80) a I s - N-N stretching (89) a I 1319 vs 1331 C-NH 2 stretching (91) a I 1316 s 1312 vw 1311 C-O stretching (86) a I vs 1289 C-O stretching (87) a I 1280 vs C-O stretching (85) a I 1270 vs C-OH stretching (80) a I 1260 s O-H in-plane bending (65) a I vw 1234 N-H in-plane bending (77) a I 1210 vw C-H in-plane bending (96) a I 1184 vw N-H in-plane bending (97) a I 1160 m C=S stretching (93) a I m 1170 C-N in-plane bending (66) m - - CH 3 rocking a I 1070 m C-H in-plane bending (65) a I ms 1084 C-C-C in-plane bending (69) a I w 1023 N-C-N in-plane bending (70) a I m 1019 C-H in-plane bending (70) a I ms 994 C-H in-plane bending (63) Contd.

5 KRISHNAKUMAR & BALACHANDRAN: NORMAL COORDINATE ANALYSIS 317 Table 2 Vibrational assignments of 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone along with calculated frequencies (in cm -1 ) and potential energy distribution Contd. Species FTIR* frequency and FT-Raman frequency and Calculated frequency Assignments (%) PED a I 980 m 972 C-C-C in-plane bending (84) a I w 953 C-C-C trigonal bending (95) a I 935 s 928 C-H in-plane bending (88) a II 933 w 934 w 927 C-N out-plane bending (60) a II 926 vs C-H out-plane bending (69) a I 923 m 924 ms 911 C-N in-plane bending (75) a I 902 w 913 w 893 C-C-C in-plane bending (92) a II vw 878 N-H out-plane bending (48) a II 880 w C-H out-plane bending (59) a II 810 m C-H out-plane bending (61) a II vw 749 C-H out-plane bending (69) a II ms 732 C-H out-plane bending (77) a II 720 vw 725 vw 698 C-C-C out-plane bending (64) a II 707 w 717 C-C out-plane bending (93) a II s 685 C-C-C out-plane bending (64) a I m 617 C-C in-plane bending (75) a II 613 m 616 C-C-C out-plane bending (57) a II m 589 N=C-H out-plane bending (55) a I 580 m 572 C-OH in-plane bending (74) a II w 551 C-C-N out-plane bending (56) a I s 535 N-C-N in-plane bending (50) a I 500 m 525 s 496 C-OCH 3 in-plane bending (49) a I m 455 C-C in-plane bending (66) a I 452 w 452 vw 447 C-N in-plane bending (65) a II 450 w C-C out-plane bending (60) a I 446 w C-N-N in-plane bending (47) a II 440 s C-C out-plane bending (62) a II 430 m O-H out-plane bending (52) a II vw 415 C-N out-plane bending (54) a II m 382 N-C=S out-plane bending (62) a II vw 387 C-N-H out-plane bendin g(59) a I vw 356 C-N-N in-plane bending (40) vw - NH 2 twisting a II vw 324 C-C=N out-plane bending (50) a I ms 321 C-NH 2 in-plane bending (67) a II vw 302 C-OH out-plane bending (50) a II m 248 N-C-N out-plane bending(54) a II vw 149 C-C-O out-plane bending (48) * Spectral data taken from Ref.6

6 318 INDIAN J PURE & APPL PHYS, VOL 42, MAY 2004 and they are listed in Table 2. The predominant PED values obtained in the normal coordinate analysis calculations are also supporting the assignments proposed in this study for the hydroxy group of 2- hydroxy-3-methoxybenzaldehyde thiosemicarbozone. 3.4 C-H Vibrations The heteroaromatic structure shows the presence of C-H stretching, in-plane bending and out-of-plane bending vibrations in the regions cm -1, cm -1, and cm -1 respectively. In this region the bands are not affected appreciably by the nature of the substituents. The FTIR bands at 3165, 3125, 3032, 3020, 2925, and 2870cm -1 and FT-Raman bands at 3160, 3110, 3080, 2926 and 2863 cm -1 in 2- hydroxy-3-methoxybenzaldehyde thiosemicarbozone is assigned to C-H stretching modes. The bands at 1210, 1070, 1026, 1000 and 935 cm -1 have been assigned to C-H in-plane bending vibrtational modes. The C-H out-of-plane bending vibrations have been found at 926, 880, 810, 765 and 744 cm -1. These observations are in good agreement with the literature values 10, N-H Vibrations The IR and Raman bands identified at 3360, 3347 cm -1 and 3382cm -1 are assigned to N-H stretching mode. The N-H in-plane bending and out-of-plane bending vibrations are found at 1220 cm -1 and 883 cm -1 respectively. These assignments are in agreement with assignments proposed by Krishnakumar et al C-N Vibrations The C=N stretching frequencies in the Raman spectrum of crystalline thiosemicarbozone 13 occur in the range cm -1. In the present investigation, the Raman bands observed at 1659, 1655 cm -1 have been assigned to C=N stretching vibrations. The IR counterparts are given in Table 2. The very strong IR peak and the strong Raman peak observed at 1544 cm -1 are assigned to C-N stretching mode. 3.7 C-O Vibrations If a compound contains the carbonyl group the absorption caused by C-O stretching is generally strongest. In 6-methoxy purine, Krishnakumar et al. 14 identified the C-O stretching frequency at 1613 and 1563 cm -1. But in this study the stretching vibrations due to C-O group attached with methyl group have been identified at 1316 cm -1 (strong-ir) and 1295 cm -1 (very strong Raman). This drift in the carbonyl group frequency of 2-hydroxy-3-methoxybenzaldehyde thiosemicarbozone is owing to the rotation of the methyl group attached at the 3 rd position of the title compound. 3.8 C-C Vibrations The carbon-carbon stretching vibrations of the title compound have been observed at 1600, 1590, 1580 and 1524 cm -1. The medium Raman bands identified at 625 and 462cm -1 have been assigned to C-C in-plane bending and the bands at 450 and 440cm -1 are assigned to C-C out-of-plane bending vibrations. These assignments are in good agreement with the literature 15. The results of the normal coordinate analysis and PED calculations are very much useful in assigning the C-C-N, C-C=N, N-C-N, N-C=S, C-N-H and C-C- O out-of-plane bending vibrations. The general agreement between the calculated and observed frequencies for both in-plane and out-of-plane bending modes is found reasonable. References 1 Yadav B S, Singh V, Kumar V et al., Commun Instrum, 5 (1997) Martin G T, Biological antagonism (Blakiston, New York), Khan M H & Giri S, Indian J Chem, 34B (1995) Rahman F, Rastogi S N, Jetley U K et al., Orient J Chem, 4 (1988) 1. 5 Yadav B S, Seema, Kumar V & Jetley U K, Indian J Pure & Appl Phys, 35 (1997) Yadav B S, Vipin Kumar & Yadav M K, Indian J Pure & Appl Phys, 36 (1998) Wilson E B, Phys Rev, 45 (1934) Schachtschneider J H, Technical Report (Shell Development Company, Everville, CA, USA) George Socrates, Infrared and Raman Characteristics Group Frequencies (John Wiley & Sons, New York) Gupta S P, Sharma S D & Jetley U K, et al., Orient J Chem, 6 (1990) Sathyanarayan D N, Vibrational Spectroscopy Theory and Applications (New Age, International, New Delhi) Krishnakumar V, Parasuraman K & Natarajan A, Indian J Pure & Appl Phys, 35 (1997) Francis R Dollish, William G Fateley & Freeman F Bentley, Characteristic Raman Frequencies of Organic Compounds (John Wiley & Sons, New York) Krishnakumar V & Ramasamy R, Indian J Pure & Appl Phys, 40 (2002) Krishnakumar V & John Xavier R, Indian J Pure & Appl Phys, 41 (2003) 95.