Conformational isomerism in cation radicals of alkylthiophens

Abstract

Radical cations containing a thiophen ring substituted by 2,5-bisalkylthio-groups have been obtained and their e.s.r. spectra interpreted in terms of unequally populated rotational isomers. Assignment of their structure has been achived by examined the effect of steric hindrance caused by bulkyl substituents on the ratio of conformers. The hyperfine splitting constants have been assigned experimentally to the asymmetric conformers, the results being in agreement with the conclusions of theoretical methods. Theoretical calculations (CNDO/2) indicate that, for these derivatives, the most populated conformation of the radical cation corresponds to the most stable rotational isomer of the neutral molecule.