Thiophen-containing radicals. Anions of isomeric dithienylethylenes

Abstract

Alkali-metal reduction of some thienylethylene derivatives at –80° yields the corresponding radical anions whose e.s.r. spectra have been interpreted by the use of deuteriated derivatives. The results indicate that phenyl and thienyl groups are locked in a definite position, on the e.s.r. time scale; rotational isomers were detected in the case of the 1,2-di-(2-thienyl)ethylene. The experimental hyperfine splitting constants could be reproduced satisfactorily by molecular orbital calculations, assuming, in the p-model framework, twisting angles of 40° for the 3-thienyl, and 0° for the 2-thienyl and phenyl groups. An analogous theoretical approach, which takes into account the participation of the 3d orbitals of sulphur, was found to disagree with the experimental results.