Base-Catalyzed Tautomerism HO: C=C +-OH enol form keto form enolate ion (vinyl alcohol) Copyright2010 Pearson Prentice Hall,Inc. In the presence of strong bases,ketones and aldehydes act as weak proton acids. A proton on the a carbon is abstracted to form a resonance- stabilized enolate ion with the negative charge spread over a carbon atom and an oxygen atom. The equilibrium favors the keto form over the enolate ion. Chapter 22 6 Chapter 22 6 Base–Catalyzed Tautomerism ▪ In the presence of strong bases, ketones and aldehydes act as weak proton acids. ▪ A proton on the a carbon is abstracted to form a resonance￾stabilized enolate ion with the negative charge spread over a carbon atom and an oxygen atom. ▪ The equilibrium favors the keto form over the enolate ion