Why is the ketone more stable than its tautomer enol?

1 Answer
anor277
Jul 8, 2017

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"#.

en.wikipedia.org

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

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