Amide conformational switching induced by protonation of aromatic substituent

Introduction of an electron-withdrawing group on the aromatic ring of N-methylacetanilide decreased the ratio of the cis conformer, and the ratio correlates well with the Hammett sigma values of the substituents. These steric properties can be applied to achieve amide conformational swiching by protonation at the aromatic substituent of 4-[bis(dimethylamino)]-N-methylacetanilide or N-[p-(dimethylamino)phenyl]-N- phenylacetamide.