Investigations of structure and conformation. Part 12. The structure of aromatic sulphonyl radicals: an e.s.r. and INDO molecular orbital study

Abstract

The e.s.r. spectra are described of a variety of arenesulphonyl radicals (ArSO₂·) which have been generated photolytically over a wide range of temperature. It is shown that the spin distribution in these σ-radicals resembles that in the benzoyl radical; radicals without ortho-substituents, which undergo relatively rapid rotation about the C–S bond at all accessible temperatures, have a(m-H) > a(o-H), a(p-H). For some di-ortho-substituted radicals, rotation around C–S is slow at low temperature (barriers to rotation have been determined for some examples) and some mono-ortho-substituted radicals demonstrate marked conformational preferences; analysis shows that the largest proton-splitting (ca. 0.2 mT) derives from the meta-proton anti to the orbital of the unpaired electron on sulphur. INDO calculations yield results in good agreement with these findings.