keto-enol tautomerism is a chemical equilibrium between two forms of a compound: the keto form, which contains a carbonyl group (C=O), and the enol form, which has a hydroxyl group (–OH) attached to a carbon-carbon double bond (C=C). This process involves the transfer of a hydrogen atom and a shift of the double bond, allowing the compound to exist in both forms. The keto form is typically more stable than the enol form due to stronger C=O bonds. However, the enol form can be significant in certain reactions, such as in the case of aldol condensation or Michael addition, where the reactivity of the enol can lead to different products.