Keto-Enol Tautomerism Tautomers are constitutional isomers Isomers are different compounds with different structures Atoms arranged differently Different from resonance structures that differ only in the position of their electrons Most carbonyl compounds exist almost exclusively in the keto form at equilibrium 0 ← H3C CH3 H3C 99.9999% 0.0001% 99.9999999% 0.0000001% Cyclohexanone AcetoneTautomers are constitutional isomers ▪ Isomers are different compounds with different structures ▪ Atoms arranged differently ▪ Different from resonance structures that differ only in the position of their electrons ▪ Most carbonyl compounds exist almost exclusively in the keto form at equilibrium Keto-Enol Tautomerism