Question #cdcfc

1 Answer
Oct 30, 2017

Here's my explanation.

Explanation:

Acetoacetic acid displays keto-enol tautomerism.

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However, the position of equilibrium depends strongly on the solvent.

The enol is the major form in nonpolar solvents, but the keto form is favoured in polar protic solvents.

Keto-enol
(Adapted from Master Organic Chemistry)

The enol form is stabilized by two factors:

  • intramolecular hydrogen bonding
  • extended conjugation

In a polar protic solvent like water or ethanol, the ketone #"C=O"# group is strongly hydrogen bonded to solvent molecules.

The lone pairs on the #"O"# atom are no longer available to stabilize the enol by hydrogen bonding.

In effect, the solvent is removing the "free" β-ketoacid as a reactant, so the position of equilibrium moves to the left to restore the equilibrium.

Thus, the enol form becomes the minor component in a polar protic solvent.