What is the relationship between ketone and enol?

1 Answer
anor277
Nov 28, 2016

An enol derivative, typically, #RC(-OH)=CH_2#, derives from a carbonyl species. It may be deprotonated to give the #"enolate"#, #RC(-O^(-))=CH_2#.

Explanation:

Carbonyl compounds typically undergo enol/ketone tautomerism, i.e. for acetone we can write:

#H_3C-C(=O)CH_3rightleftharpoonsH_2C=C(-OH)CH_3#

This equilibrium lies strongly to the left, but it may be manipulated.

The alcohol, #"the enol"#, contains a protic hydrogen, that can be potentially deprotonated to give an enolate, the anion:

#H_2C=C(-OH)CH_3+"Base"rightleftharpoonsH_2C=C(-O^(-))CH_3+"Base"""^(-)H""^(+)"#

The enolate anion itself is conceived to be in equilibrium with the carbanion:

#H_2C=C(-O^(-))CH_3rightleftharpoonsH_2^(-)C-C(=O)CH_3#.

This #"carbanion/enolate"# equilibrium is the classic strategy employed in #C-C# bond formation. Carbanions may be formed from malonic acid derivatives, and ethylacetoacetate. For more details consult your organic text.

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