Question

What is the relationship between ketone and enol?

Answer 1

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.