Title: Taft equation
Long Title: IUPAC Gold Book - Taft equation
DOI: 10.1351/goldbook.T06247
Status: current

Definition
Various equations are associated with R.W. Taft, but the term is most often used to designate the family of equations that emerged from Taft's analysis of the reactivities of aliphatic esters, and which involved the polar substituent constant \(\sigma^{\ast}\) and the steric substituent constant \(E_{\rm{s}}\): \[\log_{10}k = \log_{10}k_{0} + \rho^{\ast} \sigma^{\ast} + \delta E_{\rm{s}}\] or the one-parameter forms applicable when the role of either the polar term or the steric term may be neglected. Nowadays \(\sigma^{\ast}\) is usually replaced by the related constant \(\sigma_{I}\).

Related Terms
- <i>ρ</i>-value: https://goldbook.iupac.org/terms/view/V05019
- Hammett equation: https://goldbook.iupac.org/terms/view/H02732
- esters: https://goldbook.iupac.org/terms/view/E02219
- σ-constant: https://goldbook.iupac.org/terms/view/C05438

Source
- PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1171 (https://doi.org/10.1351/pac199466051077)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/T06247/html
- json: https://goldbook.iupac.org/terms/view/T06247/json
- xml: https://goldbook.iupac.org/terms/view/T06247/xml

Citation: Citation: 'Taft 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.T06247
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Accessed: 2026-05-10T19:48:52+00:00