Synthesis, spectral and structural studies, and an evaluation of the hydrogen bonding of some phenylhydrazones

Abstract

A series of 46 phenylhydrazones, some novel, containing a variety of structural types has been synthesised. These have been studied by ¹H n.m.r. and i.r. spectroscopy with respect to potential inter- and intra-molecular hydrogen bonding. ortho-Nitro or -carbonyl groups form strong hydrogen bonds to the imino-group which are readily observed by ¹H n.m.r. but not by i.r. spectroscopy. ‘Terminal’ carbonyl groups also form strong hydrogen bonds to the imino-group and these can be detected by both i.r. and ¹H n.m.r. spectroscopy. When both ortho-nitro- or -carbonyl groups and ‘terminal’ carbonyl groups are present the imino hydrogen atom is doubly hydrogen bonded and this is apparent in the ¹H n.m.r. spectrum. The formation of an intramolecular hydrogen bond in the phenylhydrazone prevents the formation of an intermolecular hydrogen bond between the phenylhydrazone and a polar solvent.