An electron spin resonance investigation of free radicals with oxygen- and sulphur-containing substituents

Abstract

Electron spin resonance (e.s.r.) spectra have been recorded during the photolysis of di-t-butyl peroxide in the presence of a number of organic substrates with oxygen- and sulphur-containing functional groups. By hydrogen-atom abstraction, many of the substrates yield more than one species of free radical, the relative concentrations of which have been estimated. These relative concentrations are influenced by the electrophilic character of the t-butoxyl radical, and by the stabilities of the radicals generated. Bis(methylthio)methane (2) gives rise to tris(methylthio)methyl radicals (5a), in addition to the two species expected by direct abstraction. Tris(methylthio)methane (5) gives rise to tris(methylthio)methyl radicals (5a) only, which, from the measured α¹³C hyperfine splitting constant, appear to be approximately planar. Several of the substrates used give rise to captodative free radicals. The data indicate that alkylcarbonyl groups are more effective than the methoxycarbonyl group in the capto role. The acyclic captodative radicals all exist in two distinct conformations, the likely geometries of which are discussed. Observations on two cyclic radicals suggest that relatively small deviations from a suitable planar conformation can significantly diminish the importance of the captodative effect.