Enol

Enols are chemical compounds of the general formula R1- CR2 = CR3 -OH. Your hydroxy group is weakly acidic because the negative charge of the enolate is resonance-stabilized. The simplest enol is the unstable ethenol, which rearranges immediately to acetaldehyde ( ethanal ).

In aliphatic enols equilibrium lies entirely due to the energy -favored-nation on the keto side, why enols rarely occur (for example as phosphoenolpyruvate ( PEP), the phosphoric acid ester of enolized pyruvic acid ). Aliphatic 1,3- dicarbonyl compounds are enolized stronger. So is 1,3- pentanedione ( acetylacetone ) before to 76.4 % as cis -enol, which is stabilized by an intramolecular hydrogen- bonding. Also, the cyclic enediol of ascorbic acid is almost completely in the enol form.

For the phenols, the enol form over the keto form due to the formation of an aromatic system is preferred ( see Hückel rule).