Aromatic amides. VI. Proton magnetic resonance spectra of some 2-substituted 1,3-phenylenediamines and their N,N'-diacyl derivatives

A number of 2-substituted 1,3-phenylenediamines and their N-acyl and N,N?-diacyl derivatives have been prepared and the proton magnetic resonance spectra examined for evidence that hydrogen bonding between the amide protons and the 2-substituents can occur so as to constrain two amido groups to coplanarity with the aromatic ring. The nitro and methylsulphonyl substituents behave in this way. Weaker, but still effective, dual hydrogen bonding to methoxycarbonyl, chloro, methoxy, and methylthio substituents is observed. A new technique is described for performing the Hoffman degradation of the bis-amide of 2- nitroisophthalic acid to 1,3-diamino-2-nitrobenzene.