Title: Swain–Scott equation
Long Title: IUPAC Gold Book - Swain–Scott equation
DOI: 10.1351/goldbook.S06201
Status: current

Definition
The linear free-energy relation of the form: \[\log _{10}(\frac{k}{k_{0}})=s\ n\] applied to the variation of reactivity of a given electrophilic substrate towards a series of nucleophilic reagents. \(n\) is characteristic of the reagent (i.e. a measure of its nucleophilicity) and \(s\) is characteristic of the substrate (i.e. a measure of its sensitivity to the nucleophilicity of the reagent). A scale of \(n\) values is based on the rate coefficients \(k\) for the reaction of methyl bromide with nucleophiles in water at \(25\ ^{\,\unicode{x26ac}}\rm{C}\), \(s\) being defined as 1.00 for these reactions and \(n\) being defined as 0.00 for the hydrolysis of methyl bromide. (Other scales have been devised.)

Related Terms
- electrophilic: https://goldbook.iupac.org/terms/view/E02020
- hydrolysis: https://goldbook.iupac.org/terms/view/H02902
- linear free-energy relation: https://goldbook.iupac.org/terms/view/L03551
- nucleophilicity: https://goldbook.iupac.org/terms/view/N04251
- reactivity: https://goldbook.iupac.org/terms/view/R05180
- reagent: https://goldbook.iupac.org/terms/view/R05190
- substrate: https://goldbook.iupac.org/terms/view/S06082

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1169 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/S06201/html
- json: https://goldbook.iupac.org/terms/view/S06201/json
- xml: https://goldbook.iupac.org/terms/view/S06201/xml

Citation: Citation: 'Swain–Scott equation' 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.S06201
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Accessed: 2026-05-11T13:14:55+00:00