Unstable intermediates. Part 178. The structure of intermediates formed in the radiolysis of thiols

Abstract

A wide range of thiols have been exposed to ⁶⁰Co γ-rays at 77 K both in the pure state and in dilute methanolic or aqueous glasses. Spectra assigned to RS· radicals had g_z values (z is along the C–S bond) which varied with the environment, but which were all close to 2.158 in methanol. Dissociative electron capture at sulphur (RSH + e^–→ R·+ SH^–) was only observed in methanolic or aqueous glasses, and it is postulated that solvation of the ejected SH^– ion plays an important role. The structure of a species (X) containing two sulphur atoms and having g values close to 2.058, 2.025, and 2.001 is discussed. Two rival structures, RS·–SR₂ and RSS· are considered in depth and it is concluded that the former is most probable unless both species have very similar properties. Electron loss to give RSH⁺ followed by reaction to give R(H)S·–S(H)R⁺ cations is postulated to explain certain features in the e.s.r. spectra, as an alternative to proton loss to give RS· radicals.