Term: electrophilic substitution https://doi.org/10.1351/goldbook.08167 Definition: Heterolytic reaction in which the entering group adds to a nucleophile and in which the leaving group, or electrofuge, relinquishes both electrons to its reaction partner, whereupon it becomes another potential electrophile. Note: It is arbitrary to emphasize the electrophile and ignore the feature that this is also a nucleophilic substitution, but the distinction depends on the electrophilic nature of the reactant that is considered to react with the substrate. Example: Azo coupling: <span title="reaction">\[\begin{align} \ce{RN2^{+} + H2NC6H5 -> \textit{p}\!\;{-}H2NC6H4N=NR + H^{+}}\\ \small \rm{(electrophile) \qquad (nucleophile) \quad\quad\quad \quad(electrofuge)\qquad\qquad \quad}\end{align}\]</span> Example: Array Source: PAC, 2022, 94, 353. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)' on page 412 (https://doi.org/10.1515/pac-2018-1010) Citation: 'electrophilic substitution' 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.08167 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.