Study Guides › Keto-Enol Tautomerization

Keto-Enol Tautomerization

This guide is an early version — the text is complete, and a few figures are still being redrawn. Spotted something unclear? Let us know.

The question this page answers: What is the deal with carbonyls and their enol forms?

Deeper reading: Clayden 2e: Chapter 20 Pages 449–460 — see our chapter-by-chapter practice map for Clayden.

Keto and enol forms

What is a tautomerization?

Carbonyl-containing compounds can equilibrate between electrophilic keto and nucleophilic enol forms, if there is an H α to the carbonyl.

The equilibrium between the keto and enol structural isomers is called a tautomerization:

The equilibrium between the keto and enol structural isomers is called a tautomerization:

Keto forms are typically more stable

Which tautomer dominates?

Although generally keto forms are typically more stable because the C=O π bond is more stable than the C=C one, there are a number of stable enols:

Although generally keto forms are typically more stable because the C=O π bond is more stable than the C=C one, there are a number of stable enols:

Catalyzed by either acid or base

Why is a catalyst needed?

This equilibrium between tautomers does not occur spontaneously, and must be catalyzed by either acid or base of appropriate pKa (for a reasonable equilibrium |ΔpKa| < 7):

This equilibrium between tautomers does not occur spontaneously, and must be catalyzed by either acid or base of appropriate pKa (for a reasonable equ

Spotted an error, or want a topic covered next? Let us know.