Crystallographic study of restricted rotation in o-formanilides

Article abstract of DOI:10.1007/BF01181909

The crystal structures of cis- and trans-o-methylformanilide, of its cis-thio analogue, and of trans-o-phenylformanilide have been studied with a view to clarifying the anomalously high barrier to rotation of the carbonyl group.The pair of resolved geometrical isomers is shown to be stabilized in the solid state primarily by hydrogen bonding.The increased barrier to rotation is inferred not to arise from mesomeric involvement of the carbonyl group, but from nuclear screening by the nitrogen lone pair.