Unstable intermediates

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 has gsub(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. (author)