Keto-Enol Tautomerism Mechanism of base- (b)Basic conditions 0 catalyzed enol formation Base removes the Keto tautomer The intermediate enolate acidic a hydrogen, ion,a resonance hybrid yielding an enolate ion with two resonance of two forms,can be structures. protonated either on carbon to generate the starting keto tautomer ②Protonation of the Enolate ion or on oxygen to give an enolate ion on oxygen gives the enol and 2 enol tautomer regenerates base catalyst. HO Enol tautomerMechanism of base￾catalyzed enol formation ▪ The intermediate enolate ion, a resonance hybrid of two forms, can be protonated either on carbon to generate the starting keto tautomer or on oxygen to give an enol tautomer Keto-Enol Tautomerism