An electron spin resonance study of sulphuranyl radicals of the type R2S–SX [X = CF3or R′C(O)

Abstract

Photochemically generated trifluoromethyl- or acyl-thiyl radicals add to dialkyl sulphides to form the sulphuranyl radicals R2S1–S2X [X = CF3 or R′C(O)], the e.s.r. spectra of which have been detected. These adducts appear to be non-planar at the three-co-ordinate sulphur and the unpaired electron is thought to occupy an S–S σ* orbital. The β-hydrogen splittings from the S1-alkyl groups probably arise mainly through a hyperconjugative mechanism of spin transmission and appear to depend upon the spin density (ρ) in the S1-3pσ orbital and the dihedral angle (θ) between the S1CHβ and S2S1C planes according to the approximate equation a(Hβ)= 25.2 ρcos2θ G. The g factors of the sulphuranyl radicals are markedly dependent upon temperature and the nature of R. At low temperatures, the adducts generally decay by a second-order process, presumably bimolecular self-reaction. Different behaviour is observed when R2S = [graphic omitted] or (Et2N)2S and rapid ring-opening or S–N cleavage, respectively, occurs even at low temperatures. Temperature-dependent lineshape effects are evident in the spectra of R2S–SX, and several different processes appear to be responsible for these effects, including efficient spin–rotation relaxation, conformational interconversion, and the bimolecular sulphide exchange reaction R2S + R2S–SX ⇌ R2S–SX + R2S.