Title: Zucker–Hammett hypothesis
Long Title: IUPAC Gold Book - Zucker–Hammett hypothesis
DOI: 10.1351/goldbook.Z06751
Status: current

Definition
This hypothesis states that, if in an acid catalysed reaction, \(\log _{10}k_{1}\) (first-order rate constant of the reaction) is linear in \(H_{0}\) (Hammett acidity function), water is not involved in the transition state of the rate-controlling step. However, if \(\log _{10}k_{1}\) is linear in \(\log _{10}\left[\rm{H}^{+}\right]\) then water is involved. This has been shown to be incorrect by Hammett himself.

Related Terms
- acidity function: https://goldbook.iupac.org/terms/view/A00081
- rate constant: https://goldbook.iupac.org/terms/view/O04322
- rate-controlling step: https://goldbook.iupac.org/terms/view/R05139
- transition state: https://goldbook.iupac.org/terms/view/T06468

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1176 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/Z06751/html
- json: https://goldbook.iupac.org/terms/view/Z06751/json
- xml: https://goldbook.iupac.org/terms/view/Z06751/xml

Citation: Citation: 'Zucker–Hammett hypothesis' 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.Z06751
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Accessed: 2026-06-29T09:18:57+00:00