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.