Aspects of mass spectra of organic compounds. Part XI. Rearrangements in benzoylhydrazines

Abstract

The mass spectra of N′-substituted N-benzoylhydrazines show abundant molecular ions and do not show skeletally rearranged ions. However, the diacylated hydrazine, NN′-dibenzoylphenylhydrazine, shows an unusual loss of 122 a.m.u. from the molecular ion, which involves skeletal rearrangement and loss of the elements of benzoic acid. A short study of the substituent effect on this rearrangement shows the complex competition between simple cleavage and rearrangement processes. Rearrangement of both aroyl groups is observed in some cases, which can be explained by formation of an intermediate imide, followed by 1,3-aroyl migration from nitrogen to oxygen and/or by a five-membered cyclic transition state. The mass spectra of other hydrazine derivatives showing possible 1,3-rearrangements from nitrogen to oxygen are reported, supplementing our earlier work. Some erroneous reports in the literature, where elemental compositions were incorrectly assumed, are corrected by determining them from high resolution data.