Title: 'A' value
Long Title: IUPAC Gold Book - 'A' value
DOI: 10.1351/goldbook.A00012
Status: current

Definition
The conformational preference of an equatorial compared to an axial substituent in a monosubstituted cyclohexane. This steric substituent parameter equals \(\Delta _{\rm{r}}G^{\,\unicode{x26ac}}\) in \(\pu{kcal mol-1}\) for the equatorial to axial equilibration on cyclohexane. The values are also known as 'Winstein–Holness' A values.

Related Terms
- equatorial: https://goldbook.iupac.org/terms/view/E02174
- equilibration: https://goldbook.iupac.org/terms/view/E02175

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1087 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/A00012/html
- json: https://goldbook.iupac.org/terms/view/A00012/json
- xml: https://goldbook.iupac.org/terms/view/A00012/xml

Citation: Citation: ''A' value' 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.A00012
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Accessed: 2026-05-10T19:49:50+00:00