Enol

Examples of keto-enol tautomerism

Ketone tautomerization, keto-form at left, enol at right. Ex. is 3-pentanone, a less stabilized enol.^{[citation needed]}

Enolate resonance structures, schematic representation of forms (see text regarding molecular orbitals); carbanion form at left, enolate at right; Ex. is 2-butanone, also a less stabilized enol.^{[citation needed]}

Ketone tautomerization, enol-form at left, keto at right. Ex. is 2,4-pentanedione, a hydrogen bond (---) stabilized enol.^{[citation needed]}

Aldehyde tautomerization, enol-form at left, "keto" at right; Ex. is tartronaldehyde (reductone), an enediol-type of enol.^{[citation needed]}

In organic chemistry, alkenols (shortened to enols) are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond (C=C−OH). The terms enol and alkenol are portmanteaus deriving from "-ene"/"alkene" and the "-ol" suffix indicating the hydroxyl group of alcohols, dropping the terminal "-e" of the first term. Generation of enols often involves deprotonation at the α position to the carbonyl group—i.e., removal of the hydrogen atom there as a proton H⁺. When this proton is not returned at the end of the stepwise process, the result is an anion termed an enolate (see images at right). The enolate structures shown are schematic; a more modern representation considers the molecular orbitals that are formed and occupied by electrons in the enolate. Similarly, generation of the enol often is accompanied by "trapping" or masking of the hydroxy group as an ether, such as a silyl enol ether.^[1]

Keto–enol tautomerism refers to a chemical equilibrium between a "keto" form (a carbonyl, named for the common ketone case) and an enol. The interconversion of the two forms involves the transfer of an alpha hydrogen atom and the reorganisation of bonding electrons. The keto and enol forms are tautomers of each other.^[2]