An Infrared Spectroscopic Study of the Carbonyl Stretching Frequency in a Group of Ortho and Para Quinones

This paper reports on an experimental study of the C=O stretching vibration frequency in a large number of quinonoid compounds, both substituted and unsubstituted. For nonsubstituted ortho and para quinones, relationships between the carbonyl frequency and (a) the number of fused rings, (b) the oxidation-reduction potential, and (c) the index of free valence on the parent hydrocarbon are pointed out and discussed. It is shown that for a six-atom quinonoid ring the C=O frequency is, to a first approximation, a function of the C=O bond order. For substituted quinones, the variation in the carbonyl frequency is related to the induction effect of the substituent in the same way as is the variation in oxidation-reduction potential. Certain hydroxy-substituted quinones show spectral anomalies which do not seem to fit into the usual category of hydrogen bonded compounds.