An electron spin resonance study of sulphuranyl radicals of the type R2S–SX [X = CF3 or 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 S¹-3p_σ orbital and the dihedral angle (θ) between the S¹CH_β and S²S¹C planes according to the approximate equation a(H_β)= 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.