extended Hammett equation

https://doi.org/10.1351/goldbook.E02279
This term applies in a general way to any multiparametric extension of the Hammett equation. It is sometimes used specifically for a form of dual substituent-parameter equation in which the actual value of the correlated property P under the influence of the substituent X is used, rather than the value relative to that for X = H. An intercept term h corresponding to the value of P for X = H is introduced, e.g. P=α σI+β σR+h The equation may be applied to systems for which the inclusion of further terms to represent other effects, e.g. steric, is appropriate.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1114 [Terms] [Paper]
Citation: 'extended Hammett 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.E02279 RIS BibTex EndNote
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