Vibrational Overtone Spectroscopy of Pyridine and Related Compounds.

摘要

The vibrational overtone spectra of gaseous pyridine, 3-fluoropyridine, 2,6-difluoropyridine. and pyrazole have been recorded using photoacoustic absorption spectroscopy. The pyridine, 3-fluoropyridine, and 2,6-difluoropyridine overtone spectra exhibit two local mode progressions. These CH local modes are mixed and cannot be assigned to the separate CH oscillators at the 2,6 and 3,4 and 5 positions. The transition wavenumbers and peak widths are compared to those of benzene and pyrrole, both of which exhibit only one overtone peak at each quantum level. The fourth overtone spectrum of gaseous pyrazole displays two peaks. These spectra indicate that the presence of a lone pair perpendicular to the aromatic pi system in aromatic heterocycles removes the local mode equivalency of the CH oscillators.