Enols

Enol is a redirect to this article. For more see ENOL .

Keto-enol tautomerism using acetone as an example: 99.9998% of the keto (left) and 0.0002% of the enol (right) form are present in equilibrium.

Enols are chemical compounds of the general formula R ¹ -CR ² = CR ³ -OH. Its hydroxyl group is weakly acidic because the negative charge of the enolate is mesomerically stabilized . The simplest enol is the unstable ethenol , which immediately rearranges to acetaldehyde (ethanal) .

The ascorbic acid is a stable enol.

In the case of aliphatic enols, the equilibrium is completely on the keto side because of the energetic advantage, which is why enols only occur as derivatives - for example as phosphoenolpyruvate (PEP), the phosphoric acid ester of enolized pyruvic acid . However, aliphatic 1,3-dicarbonyl compounds are more enolized. For example, 76.4% of 2,4-pentanedione ( acetylacetone ) is present as cis -enol, which is stabilized via an intramolecular hydrogen bond . The cyclic enediol ascorbic acid is also almost entirely in the enol form.

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

See also

• Enolates
• Reductones
• Keto-enol tautomerism

Individual evidence

1. ^ ^{A b} Siegfried Hauptmann : Organic Chemistry , 2nd edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig 1985, ISBN 3-342-00280-8 , p. 377.