05185 IUPAC Gold Book - reactivity index 10.1351/goldbook.R05185 R05185 current 1 Any numerical index derived from quantum mechanical model calculations that permits the prediction of relative reactivities of different molecular sites. Many indices are in use, based on a variety of theories and relating to various types of reaction. The more successful applications have been to the substitution reactions of conjugated systems where relative reactivities are determined largely by changes of $\ce{\uppi\!\mbox{-}electron}$ energy. conjugated systems https://goldbook.iupac.org/terms/view/C01267 substitution reactions https://goldbook.iupac.org/terms/view/S06078 PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1159 (https://doi.org/10.1351/pac199466051077) https://goldbook.iupac.org/terms/view/R05185/html https://goldbook.iupac.org/terms/view/R05185/json https://goldbook.iupac.org/terms/view/R05185/plain Citation: 'reactivity index' 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.R05185 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. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . 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. 2026-05-11T15:04:41+00:00