05243 IUPAC Gold Book - regioselectivity 10.1351/goldbook.R05243 R05243 current 1 A regioselective reaction is one in which one direction of bond making or breaking occurs preferentially over all other possible directions. Reactions are termed completely (100%) regioselective if the discrimination is complete, or partially (x%), if the product of reaction at one site predominates over the product of reaction at other sites. The discrimination may also semi-quantitatively be referred to as high or low regioselectivity. (Originally the term was restricted to addition reactions of unsymmetrical reagents to unsymmetrical alkenes.) In the past, the term 'regiospecificity' was proposed for 100% regioselectivity. This terminology is not recommended owing to inconsistency with the terms stereoselectivity and stereospecificity. addition https://goldbook.iupac.org/terms/view/A00133 alkenes https://goldbook.iupac.org/terms/view/A00224 chemoselectivity https://goldbook.iupac.org/terms/view/C01051 stereoselectivity https://goldbook.iupac.org/terms/view/S05991 stereospecificity https://goldbook.iupac.org/terms/view/S05994 PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1160 (https://doi.org/10.1351/pac199466051077) https://goldbook.iupac.org/terms/view/R05243/html https://goldbook.iupac.org/terms/view/R05243/json https://goldbook.iupac.org/terms/view/R05243/plain Citation: 'regioselectivity' 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.R05243 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. 2026-05-10T05:20:35+00:00