Term: Swain–Scott equation
https://doi.org/10.1351/goldbook.S06201

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°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:
1) linear free-energy relation (http://doi.org/10.1351/goldbook.L03551).
2) reactivity (http://doi.org/10.1351/goldbook.R05180).
3) electrophilic (http://doi.org/10.1351/goldbook.E02020).
4) substrate (http://doi.org/10.1351/goldbook.S06082).
5) nucleophilicity (http://doi.org/10.1351/goldbook.N04251).
6) reagent (http://doi.org/10.1351/goldbook.R05190).
7) hydrolysis (http://doi.org/10.1351/goldbook.H02902).

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)

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. https://doi.org/10.1351/goldbook.S06201

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