4-(4-Methoxyphenylamino)-3-phenyl-azo-3-penten-2-one

The title compound, C18H19N3O2, was obtained by an azocoupling reaction wit h enaminones and is composed of a planar azoenamine skeleton which forms a six-membered ring through a symmetrical intramolecular hydrogen bond. The c ompound was found to exist as an equilibrium mixture of major hydrazoimino and minor azoenamine tautomers. Quantircation of the relative contribution of the tautomeric forms is obscured by the existence of the hydrogen bond. Comparison of the results with those obtained for a similar structure revea led a substantial effect on the tautomeric equilibria of the nature of the substituent bonded to the amine nitrogen.