FAR INFRARED AND RAMAN VAPOR PHASE SPECTROSCOPY OF HETEROCYCLIC COMPOUNDS

Author Institution: National Institute for Petroleum and Energy Research; National Institute for Petroleum and Energy ResearchThe vapor phase vibrational spectra of quinoline, isoquinoline, benzofuran, N-methylpyrrole, and 2,5-dimethylpyrrole were examined by Fourier transform infrared and Raman spectroscopy. Quinoline, isoquinoline, and benzofuran vapor Raman spectra of the lowest vibrational modes revealed distinct O, Q, and S branch contours. In addition, these compounds displayed an unusual cluster of bands in the $450-300 cm^{-1}$ region which were resolved and assigned to various combinations and overtones of the lower fundamentals. Several spectral differences were observed between the liquid and vapor phases of these heterocyclics. Both the intensities and frequencies of several low frequency modes changed dramatcally. These vapor phase out-of-plane modes are sometimes red-shifted from their liquid frequency values by as much as $20 cm^{-1}$. The ideal gas thermodynamic entropies were calculated and compared with calorimetrically determined entropies. The effect of the vapor-liquid spectral shifts on thermodynamic calculations can be significant and will be discussed.