Structure of aromatic diazocyanides; synthesis of diazoisocyanides

Abstract

I.r. spectra of a number of aromatic diazocyanides, prepared under conditions that facilitate isolation and spectral analysis of pure isomeric forms, suggest that extant published data refer to stable isomers only. Substantial differences between the spectra of unstable and stable isomers permitted the quantitative determination of these forms in mixtures and allowed the kinetics of isomerization of unstable to stable forms to be studied.

Although the results from i.r. analysis of aromatic diazocyanides are consistent with the concept of geometric isomerism of these molecules, the long-standing uncertainties concerning the type of isomerism could only be settled finally by synthesis of diazoisocyanides. p-Chloro- and p-bromo-benzenediazoisocyanides exhibit properties, including vibrational and electronic spectra, entirely different from those of the corresponding diazocyanides. Detailed analysis of the i.r. spectra of a number of p-halogeno-benzenediazoisocyanides leads to the conclusion that the diazoisocyanide molecule may be represented as a hybrid of two canonical forms.