Enol

Enols (also known as alkenols) are alkenes with a hydroxyl group affixed to one of the carbon atoms composing the double bond. Alkenes with a hydroxyl group on both sides of the double bond are called enediols. Deprotonated anions of enols are called enolates. A reductone is a compound that has an enediol structure with an adjacent carbonyl-group.

Quotes

• In the enolate ion, the inductive effect of the positively polarized carbonyl carbon strongly stabilizes the negative charge at the a-position. Aldehydes are stronger acids than ketones because their carbonyl carbon bears a larger partial positive charge (...) Further strong stabilization is provided by delocalization of charge onto the electronegative oxygen, as described by the resonance forms just pictured. The effect of delocalization is also refl ected in the electrostatic potential map of the acetone enolate shown in the margin (on an attenuated scale), which exhibits negative charge (red) on the a-carbon as well as on the oxygen. An example of enolate formation is the deprotonation of cyclohexanone by lithium diisopropylamide (LDA; Section 7-8).
  • K. Peter C. Vollhardt, Neil E. Schore (2011) Organic chemistry : structure and function 6th ed. Ch. 18 : Enols, Enolates, and the Aldol Condensation

• The hydrogens on the carbon next to the carbonyl group in aldehydes and ketones are acidic, with pK_a values ranging from 16 to 21. Deprotonation leads to the corresponding enolate ions, which may attack electrophilic reagents at either oxygen or carbon. Protonation at oxygen gives enols.
  • K. Peter C. Vollhardt, Neil E. Schore (2011) Organic chemistry : structure and function 6th ed. Ch. 18 : Enols, Enolates, and the Aldol Condensation