keto-enol tautomerism

Keto-enol tautomerism is a chemical phenomenon where a compound exists in two or more forms that can readily interconvert. This interconversion often involves the migration of a hydrogen atom between two other atoms, changing the position of a double bond. The most common type is the equilibrium between a keto compound and an enol compound.1

In this process, a hydrogen atom shifts from a carbon atom adjacent to a carbonyl group (the alpha-carbon) to the oxygen atom of the carbonyl group. Simultaneously, the double bond moves to the alpha-carbon. This results in two isomeric forms: the keto form and the enol form.2

While both forms are present, the keto form is typically more stable and predominant in simple cases, such as acetaldehyde. However, the equilibrium between these forms is dynamic, with molecules rapidly converting between keto and enol states. This interconversion is crucial for certain chemical reactions involving carbonyl compounds. Some compounds, like ethyl acetoacetate, exist in a significant ratio of both keto and enol forms, especially when stabilized by factors like hydrogen bonding.21