Question

Why is the ketone more stable than its tautomer enol?

Answer 1

Well, sometimes it's not..........but enol formation in `"1,3-diketones"` and `"1,3-diesters"` is facilitated by the formation of a stable, heterocylic six-membered ring that is stabilized by hydrogen bonding.........

Explanation:

You know that ketones, and aldehydes, undergo some degree of `"keto-enol tautomerism"`:

`RCH_2C(=O)CH_2RrightleftharpoonsRCH=C(-OH)CH_2R`

Sometimes, this equilibrium can be driven towards the RHS, the enol side by treating the starting material with a strong base to form the `"enolate"`.

In general for `"1,3-dicarboxylic acid derivatives"`, the equilibrium lies substantially to the right........

`"RO(O=)CCH"_2"C(=O)OR"rightleftharpoons"RO(O=)CCH=C("-"OH")"OR"`

This so-called `"enol"` `"RO(O=)CCH=C("-"OH")"OR"` contains an acidic hydrogen, and upon deprotonation this forms the basis for many `C-C` bond formation reactions as a so-called `"carbanion"`. In your organic text there will be a whole chapter on `"carbanions and enolates"`.

And in the diagram enol formation is facilitated by the formation of a stable, heterocylic six-membered ring that is stabilized by hydrogen bonding.........