Raman and infrared spectra of tere-phthalaldehyde

Transcription

1 Pram[qa, Vol. 18, No. 4, April 1982, pp ~) Printed in India. Raman and infrared spectra of tere-phthalaldehyde R A YADAV, RAMAKANT, P C MISHRA and I S SINGH Spectroscopy Laboratory, Department of Physics, Banaras Hindu University, Varanasi , India MS received 3 October 1981; revised 14 December 1981 Abstract. The laser Raman spectrum of tere-phthalaldehyde powder has been recorded on a Jobin Yvon no 2S speetrophotometer with a~100 mw Argon-Ion laser. The infrared spectrum of the solid substance has been recorded on a Perkin-Elmer 621 spectrophotometer in the region cm -1 using KBr and nujol mull techniques. The observed frequencies have been assigned in terms of the fundamentals, overtones and combinations assuming D~a point-group symmetry. Keywords. Infrared spectrum; Raman spectrum; vibrational assignment. 1. Introduction Benzaldehyde and its mono-substituted derivatives have been the subject of extensive studies. Consequently, sufficient data on the vibrational frequencies of monosubstituted derivatives of benzaldehyde are available in the literature. The infrared spectrum of phthalaldehyde has been studied by Pinchas (1957) and Lal et al (1971). Srivastava et al (1972) have analysed the infrared spectrum of iso-phthalaldehyde. But neither the Raman nor the infrared spectrum of tere-phthalaldehyde seems to have been reported in the available literature so far. In the present investigation we report the results and analysis of the Raman and infrared spectra of tere-phthalaldehyde. 2. Experimental The chemical, of pure grade, was obtained from Fluka Co. and was used without any further purification. The substance is solid at room temperature. The infrared spectrum (figure 1) was recorded on a Perkin-Elmer 621 spectrophotometer in the region cm -1 using KBr and nujol mull techniques. The Raman spectrum (figure 2) of powdered substance was recorded on a Jobin Yvon HG 2S spectrophotometer using a,~100 mw Argon-Ion laser source. Due to high level of fluorescence emission, the measurement of depolarization was not possible. 3. Results and discussion The molecule tere-phthalaldehyde would belong to D2~ point group, if the two CliO groups are taken to be coplanar with the phenyl ring and are assumed to be mutually 311

2 312 R A Yadav et al 1OO[ I Tere- phthaloldehyde i - "2 NBr p e ~ A O 1OO N OI mull I 0 1OOO Frequency (crn-11 I R spectrum Figure I. ~'~~"'v~.- phthalaldehyde... T r~~v~pt,,b e p ~'a" 4000 I l I I OOO Frequency (cm-1] Figure 2. Raman spectrum ( powder/ non-interacting. Forty-two normal modes of vibrations are distributed among the various species as: 8ag + 2big + 4br + 7bsg + 3a, + 7bz. + 7b~. + 4bz, but thirty normal modes of vibrations of the molecule p-x CrH4X are distributed among the species of the D~h point group as: 6ag + lbzo q-- 3b2o + 5b3g + 2a. -k- 5bl. + 5b2. + 3b3. Thus the two CHO groups would give rise to 12 normal modes of vibrations as" 2ag + lbzo + lb~g + 2b30 + la. -k 2bx. + 2b2. + lbs.. The vibrations of species a s and bo's are Raman active (vibrations of species ag being polarized and those of bg's being depolarized) and the vibrations of the species b,'s are infrared active, whereas the vibrations of the species a, are inactive. The molecule tere-phthalaldehyde consists of two parts (i) phenyl ring and (ii) CHO groups. Therefore, it must show the characteristic frequencies of both the parts. Two CHO groups, being in para-position, are so widely separated that the interaction between their internal vibrations can be ignored. Therefore, the internal vibrations of the two CHO groups would have nearly equal frequencies.

3 Raman and infrared spectra of tere-phthalaldehyde 313 Phenyl ring as well as CHO group vibrations being separately discussed by earlier workers, need no further discussion. Assignments have been made on the basis of magnitudes and relative intensities of the observed frequencies in the Raman and infrared spectra. Assistance ~as also been taken from the assignments made for related molecules (Brown 1967; Garg ; Lal et al 1971, 1973; Padhye and Viladkar 1960; Pinchas 1957; Singh and Singh (1967, 1968a, b, ), Srivastava et al (1969, , 1972). Varsanyi's (1969) convention of the heavy and light substituents has also been taken into account. Most of the observed frequencies have been assigned as fundamentals. In assigning the combination frequencies the infrared frequencies observed in the nujol mull are preferred as compared to those observed in the KBr (if there is a choice). The observed frequencies along with their relative intensities in the Raman and infrared spectra and tentative assignments are presented in table 1. Table 1. Observed frequencies and their proposed assignments. Raman powder Freq. Rel. (cm-i) int. (I) (2) Infrared KBr pellet Nujol mull Proposed Freq. Rel. Freq. Rel. assignments (era -x) int. (cm -1) int. (3) (4) (5) (6) (7) ClIO torsion C--CHO o.p. bending C--CHO o.p. bending C--CHO i.p. bending C-- C- C o.p. bending C-C-C i.p. bending C--CHO i.p. bending C=O o.p. bending C=O o.p. bending C--C--C i.p. bending C--C--C i.p. bending C--C--C o.p. bending C--H o.p. bending C-- C stretching (ring breathing) C=O i.p. bending C=O i.p. bending C--H o.p. bending C--H o.p. bending C--H o.p. bending C--H i.p. bending C--H i.p. bending C- CHO stretching (*) C--H i. p. bending C- CHO stretching C-H i.p. bending

4 314 R A Yadav et al Table 1. (Contd.) (1) (2) (3) (4) (5) (6) (7) C - H i.p. bending C--H i.p. bending 24 C = C stretching C=C stretching C=C stretching C = C stretching C= C stretching 97 C=O stretching C=O stretching C-- H stretching C--H stretching C-- H stretching C--H stretching N.B. 1. i.p. = in-plane, o.p. = out of plane, Rel. int. = Relative intensity, * = Our proposal. Acknowledgements The authors are very grateful to the Director, RSIC, IIT, Powai, Bombay, for permission to use Jobin Yvon rig 2S spectrophotometer. They are also thankful to Prof.

5 Raman and infrared spectra of tere-phthalaldehyde 315 G B Singh, for permission to use Perkin-Elmer 621 spectrophotometer. authors (RAY) is thankful to csm, New Delhi, for financial assistance. One of the References Brown F B 1967 Spectrochim. Acta A Garg S N J. ScL Res., B.H.U., India 4 68, 83 Lal B B, Srivastava M P and $ingh I S 1971 Indian J. Pure Appl. Phys Lal B B, $dvastava M P and Singh I S 1973 Indian J. Pure Appl. Phys Padhye M R and Viladkar B G 1960 J. Sci. Res., B.H.U., India B19 45 Pinchas S 1957 Analyt. Chem Singh V B and Singh I S 1967 Curr. Sci $ingh V B and $ingh I S 1968a Indian J. Pure dppl. Phys. 6 81,682 Singh V B and $ingh I S 1968b Indian J. Phys Singh V B and $ingh I S d. Sci. Res., B.H.U., India 20(1) 5 $dvastava M P, Lal B B and Singh I $1972 Indian J. Pure Appl. Phys. 10, 570 Srivastava M P, Singh O N and Singh I $1969 Indian J. Pure Appl. Phys. 7 4 Srivastava M P, $ingh O N and Singh I $ J. Sci. Res., B.H.U., India 20(2) 158 Varsanyi G 1969 Vibrational spectra of benzene derivatives (New York: John Wiley & Sons)