Keto-Enol Tautomers(2) Tautomerism is also catalyzed by acid. ·In acid: Step 1:Protonation on O Step 2:Deprotonation on C H H.O: HO: HO+ >c=C+H,0 keto form protonated carbonyl enol form Copyright 2005 Pearson Prentice Hall,Inc. => Chapter 22 6Chapter 22 6 Keto-Enol Tautomers (2) • Tautomerism is also catalyzed by acid. • In acid: =>