An electron spin resonance study of 1-alkylthioallyl, 3-alkylthiopropynyl, and alkylthioalkyl radicals:An examination of spin delocalization by alkylthio groups

E.s.r. spectra have been recorded for CH2CHĊHSBu t and HC≡CĊHSBut. The hyperfine splitting constants indicate that considerable spin density is delocalized onto the SBut group. This group is a more effective acceptor of spin than alkyl, hydroxy, or alkoxy substituents, and comparable with that of an ethynyl substituent. The barrier to rotation about the Cα-S bond in AdSĊH2 is greater than that about the Cα-O bond in AdOĊH2 as a consequence of greater spin delocalization onto sulphur than onto oxygen. The mechanism of reaction of t-butoxyl radicals with sulphides is discussed. The ButSĊHCH2OCH3 radical exists in an eclipsed conformation whereas ButSĊHCH 2Ph and CH3OĊHCH2Ph prefer staggered conformations.