Conformational analysis in heteroaromatic carbonyl compounds. Part I. Radical anions of thiophen-2,5-dicarbaldehyde and related derivatives

Abstract

The room-temperature e.s.r. spectrum of the photolytically generated radical anion of thiophen-2,5-dicarbaldehyde shows the existence of two of the three possible rotational isomers. The less stable could be straightforwardly identified as the O-cis–trans because of the non-equivalence of the thiophen proton splittings. Examination of a number of derivatives having different steric requirements allowed the assignment of the O-cis–cis conformation to the other rotamer.