4-(4-Methoxyphenylamino)-3-phenylazo-3-penten-2-one.

The title compound, C18H19N3O2, was obtained by an azo-coupling reaction with enaminones and is composed of a planar azoenamine skeleton which forms a six-membered ring through a symmetrical intramolecular hydrogen bond. The compound was found to exist as an equilibrium mixture of major hydrazoimino and minor azoenamine tautomers. Quantification 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 revealed a substantial effect on the tautomeric equilibria of the nature of the substituent bonded to the amine nitrogen.