Conformational preferences of 3,3′-dithienyl-methane

The conformation of 3,3′-dithienyl-methane (DTM) has been investigated by means of quantum-mechanical MINDO/3 calculations in conjunction with analysis of dipole moment data obtained in benzene solution. The results rule out free rotation and there is a clear preference for the twisted conformations (75°, 75°) and (75°, 285°), the former being energetically more favourable and corresponding to a cis-trans arrangement of the rings. Easy interconversion between these conformers may occur via concerted rotation of the rings. Analysis in terms of a Fourier-type expansion of the internal rotation potential function shows the predominance of the hyperconjugative interactions in determining the conformational features of DTM.