Conformational preference in thiophene-2-carbaldehyde

The 100 MHz ¹H NMR spectra of thiophene-2-carbaldehyde have been obtained in different solvents and analysed. It was found that the SO-cis conformation is more stable in all solvents, and that the proportion of the SO-trans population increases with decreasing polarity of the solvent. CNDO/2 calculations predict that the SO-cis is more stable than the SO-trans conformation. The aldehyde coupling to the ring was calculated by the CNDO/2 method and compared with the experimental value.