Acylarylnitrosamines. Part I. Electron spin resonance studies relevant to the mechanism of decomposition of acylarylnitrosamines in various solvents

Abstract

An e.s.r. spectroscopic investigation of a wide series of acylarylnitrosamines in several series of solvents has been carried out. In general the signals were either, or both, of two types: those of the PAPN type [ArN(NAr·Acyl)·O·], and in this Chalfont and Perkins' assignment of structure is confirmed, and those of the (phenylazo)oxyl σ-radical type (PhNNO·). These assignments have been established by study of the effect of variation of substituents on the resulting spectra, by theoretical calculations and by computer simulation in selected cases. The constancy of appearance of the (phenylazo)oxyl radical compared with the absence of PAPN in some cases (e.g. mesitylene) but not in others (e.g. benzene) suggests that the former is the more significant chain carrying radical in the decomposition of acylarylnitrosamines in such solvents. It is also concluded that electron transfer involving the diazonium cation and the intermediate arylcyclohexadienyl radical cannot be ruled out as a key step in the decomposition. The identification and mechanistic significance of other signals observed in ether and cumene are discussed.