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

The e.s.r. spectra of a variety of photochemically generated thiophene-2-sulphonyl radicals are described. Their spin distribution is typical of a-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 n-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 SO,and heteroaromatic moieties.