05980 IUPAC Gold Book - stereogenic unit 10.1351/goldbook.S05980 S05980 current synonyms: stereogen, stereoelement 1 A grouping within a molecular entity that may be considered a focus of stereoisomerism. At least one of these must be present in every enantiomer (though the presence of stereogenic units does not conversely require the corresponding chemical species to be chiral). Three basic types are recognized for molecular entities involving atoms having not more than four substituents: A grouping of atoms consisting of a central atom and distinguishable ligands, such that the interchange of any two of the substituents leads to a stereoisomer. An asymmetric atom (chirality centre) is the traditional example of this stereogenic unit. A chain of four non-coplanar atoms (or rigid groups) in a stable conformation, such that an imaginary or real (restricted) rotation (with a change of sign of the torsion angle) about the central bond leads to a stereoisomer. A grouping of atoms consisting of a double bond with substituents which give rise to cis-trans isomerism. asymmetric https://goldbook.iupac.org//terms/view/A00478 central atom https://goldbook.iupac.org//terms/view/C00930 chiral https://goldbook.iupac.org//terms/view/C01057 chirality centre https://goldbook.iupac.org//terms/view/C01060 cis-trans isomerism https://goldbook.iupac.org//terms/view/C01093 conformation https://goldbook.iupac.org//terms/view/C01258 enantiomer https://goldbook.iupac.org//terms/view/E02069 ligands https://goldbook.iupac.org//terms/view/L03518 stable https://goldbook.iupac.org//terms/view/S05900 stereoisomerism https://goldbook.iupac.org//terms/view/S05983 torsion angle https://goldbook.iupac.org//terms/view/T06406 PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2219 (https://doi.org/10.1351/pac199668122193) https://goldbook.iupac.org/terms/view/S05980/html https://goldbook.iupac.org/terms/view/S05980/json https://goldbook.iupac.org/terms/view/S05980/plain Citation: 'stereogenic unit' 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.S05980 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. 2026-06-07T11:01:13+00:00