Enol

The enol form is shown on the left. It is usually unstable, does not survive long, and changes into the keto (ketone) form, shown on the right. This is because Oxygen is more Electronegative than Carbon and thus forms stronger multiple Bonds . Hence, a carbon-oxygen ( Carbonyl ) double bond is more than twice as strong as a carbon-oxygen single bond, but a carbon-carbon double bond is weaker than two carbon-carbon single bonds.

Only in 1,3 dicarbonyl and 1,3,5 tricarbonyl compounds does the (mono)enol form predominate. This is because Resonance and ''intra''molecular Hydrogen Bond ing occur in the enol form but are not possible for the keto form. Thus, propanedial (OHCCH₂CHO) exists to an extent of over 99 percent as the monoenol. The proportion is lower for 1,3 aldehyde ketones and diketones. The enol (and enolate) are an important intermediate for many organic reactions.

The words enol and '''alkenol''' are combinations of the words '''alkene''' (or just -ene , the suffix given to Alkene s) and ''' Alcohol ''' (which represents the enol's hydroxyl group).

Enolate ion

When the hydroxyl group (−OH) in an enol loses a hydrogen ion (H⁺), a negative enolate ion is formed as shown here:

Enolates can exist in quantitative amounts in strictly Brønsted acid free conditions, since they are generally very basic.

1,3 dicarbonyl and 1,3,5 tricarbonyl compounds are quite acidic because of the strong resonance stabilization created when one of the hydrogens is removed (from either the keto or enol forms). The resonance from the enol is exactly analogous to that used to explain the acidity of Phenols and consists of the delocalisation of the negative charge of the enolate ion to the alpha-carbon. These enolate ions are very valuable in synthesis of complicated alcohols and carbonyl compounds (aldol additions). The synthetic value is due to the Nucleophilicity of the enolate group, since it has a net negative charge.

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Enol