What is keto-enol tautomerism?

1 Answer
anor277 · Truong-Son N.
Aug 8, 2016

H_3C-C(=O)-CH_3 rightleftharpoons H_2C=C(-OH)-CH_3H3C−C(=O)−CH3⇌H2C=C(−OH)−CH3

Explanation:

The equation above describes keto-enol tautomerism for acetone. As written, the equilibrium lies strongly to the left. It's worth mentioning that this is NOT resonance.

This tautomerism offers a potential for C-CC−C bond formation, especially for 1,3-dicarbonyl species, where the equilibrium may lay towards the enol side.

The alcoholic (i.e. enolic) hydrogen is potentially acidic, and may be removed by a strong base, to give the enolate, which itself may give equilibrium quantities of its tautomer, the carbanion, as shown:

H_2C=C(-O^_)-CH_3 rightleftharpoons H_2^(-)C-C(=O)-CH_3H2C=C(−O_)−CH3⇌H−2C−C(=O)−CH3

For 1,3-"dicarbonyls"1,3−dicarbonyls such as "acetylacetone"acetylacetone, the enolic form is strongly favoured in that it forms a 6-membered ring stabilized by hydrogen bonding, H_3C-C(=O)CH=C(-OH)CH_3H3C−C(=O)CH=C(−OH)CH3.

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