Title: tautomer
Long Title: IUPAC Gold Book - tautomer
DOI: 10.1351/goldbook.12734
Status: current

Definition
Structural isomer that can readily convert to another form that differs only by the attachment position of a hydrogen atom and the location of double bond(s).

Note
In most cases, these isomers are formed by a proton shift to or from heteroatoms such as \(\ce{O}\), \(\ce{N}\), or \(\ce{S}\) as typified by the enol and keto forms of carbonyl compounds. Tautomers rapidly interconvert by proton transfer and are usually in equilibrium with one another.

Source
- PAC, 2013, 85, 1725. 'Glossary of terms used in medicinal chemistry. Part II (IUPAC Recommendations 2013)' on page 1753 (https://doi.org/10.1351/PAC-REC-12-11-23)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/12734/html
- json: https://goldbook.iupac.org/terms/view/12734/json
- xml: https://goldbook.iupac.org/terms/view/12734/xml

Citation: Citation: 'tautomer' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.12734
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Accessed: 2026-07-14T13:59:13+00:00