Investigations of the vibrational spectra of a number of related quinonoid and benzenoid compounds

Abstract

The vibrational spectra of a number of chloroquinones, hydro-quinones, benzenediazo-oxides and aminophenols have been recorded and complete assignments attempted. In the case of two chloroquinones, p-hydroquinone and p-aminophenol the previous assignments for these compounds have been reviewed and modified in the light of more extensive experimental data, such as information obtained from the far infrared region, comprehensive Raman spectra and deuteration experiments. The planar and non-planar vibrational frequencies of parabenzo-quinone have been calculated using various sets of zero-order force constants. Using a least squares method the refinement of the initial sets of force constants was carried out with the help of the observed frequencies of parabenzoquinone and some of its deuterated derivatives. The resulting sets of force constants were used to calculate the vibrational frequencies of other compounds considered in this work. The potential energy distribution and Cartesian displacement figures calculated from these and other zero-order force fields have been used to aid the assignment of the spectra. The n.m.r. spectra of some of the compounds considered here have been recorded and a complete analysis of the spectrum of p-benzene-diazo-oxide has been carried out.