Acid-Catalyzed Tautomerism HO: HO: C=C+H,0 keto form protonated carbonyl enol form Copyright 2010 Pearson Prentice Hall,Inc. In acid,a proton is moved from the a-carbon to oxygen by first protonating oxygen and then removing a proton from the carbon. Chapter 22 7Chapter 22 7 Acid-Catalyzed Tautomerism ▪ In acid, a proton is moved from the a-carbon to oxygen by first protonating oxygen and then removing a proton from the carbon