EZ-isomerism in alkyl phenyl ketone phenylhydrazones and acetaldehyde phenylhydrazone

Abstract

The E- and Z-isomers of the hydrazones PhRCN·NHPh (R = Prⁱ or Bu^t) exhibit anomalous n.m.r. spectra owing to the C-phenyl group being non-coplanar with the CN bond. An improved procedure for the preparation of pure Z-acetaldehyde phenylhydrazone, the kinetically controlled product of the condensation, is described. Phenyl-hydrazine is shown to catalyse the interconversion of the E- and Z-isomers of phenylhydrazones by an addition–elimination mechanism.