Enol

An enol has an OH group bonded to a carbon of a C=C bond. Protonation and pi-bond rearrangement can interconvert it with a carbonyl compound through keto-enol tautomerism.

Interconversion of a carbonyl compound with its enol or enolate-derived forms. Reprotonation of a planar intermediate can epimerize an alpha stereocentre.

An enol stabilized by an intramolecular O–H···O interaction, commonly closing a six-membered arrangement in a 1,3-dicarbonyl compound. proton exchange between equivalent enol forms can average NMR environments.

A silyl enol ether has the connectivity $\mathrm{C}=\mathrm{C}-\mathrm{O}-\mathrm{Si}{\mathrm{R}}_3$. Nucleophilic attack at silicon can cleave the Si–O bond and generate an enolate without adding to the original carbonyl carbon.

An O-silylated ester enolate, with two oxygen substituents on one carbon of the enol double bond.

An enol carbonate is an enol derivative whose oxygen bears a carbonate ester group, represented schematically by ${\mathrm{R}}_2\mathrm{C}=\mathrm{CR}-\mathrm{O}-\mathrm{C}(=\mathrm{O})-\mathrm{O}{\mathrm{R}}^{\prime }$. The enol-derived carbon-carbon double bond and the carbonate group are both part of its reactivity.

Masking an enol as a derivative allows its structure and reactions to be controlled separately from those of the parent carbonyl compound. The exact substitution pattern therefore matters when using an enol carbonate in synthesis.