Section 17: Reaction at the α-Position to a Carbonyl Group255 Section 17: Reaction at α-Position to Carbonyl Group 17.1 Introduction 17.1.1 Tautomerization •A carbonyl compound with a hydrogen atom attached to a carbon atom α- to the carbonyl group may exist in one of two tautomeric forms: the keto-tautomer, or the enolform. RHR'R"ORR"R'OHketo- formenol form•These two structures are rapidly interconvertible (a defining quality of tautomers), but in the majority of cases, the keto- tautomer is the dominant component of the equilibrium for ketones, and even more dominant for the carboxylic acid derivatives. OOH:1OOH1x10-4:11x10-7•Note that tautomeric forms differ in the placement of their atoms: they are not resonance contributors, but distinct equilibrium species. Keto-enol tautomerization may be catalyzed by both acids and bases.
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