An investigation of structure and conformation of thiophene-2-sulphonyl radicals

Abstract

The e.s.r. spectra of a variety of photochemically generated thiophene-2-sulphonyl radicals are described. Their spin distribution is typical of σ-radicals; radicals without substituents at position 3 exhibit relatively rapid rotation about the C–S bond at all accessible temperatures while the 3-bromo-substituted ones demonstrate a marked conformational preference which has been interpreted in terms of a π-type conjugated structure. These findings are substantiated also by the results of INDO calculations carried out for the unsubstituted thiophene-2-sulphonyl radical with different relative arrangements of the SO₂ and heteroaromatic moieties.