Term: isotopically substituted https://doi.org/10.1351/goldbook.I03338 Definition: Describes a compound that has a composition such that essentially all the molecules of the compound have only the indicated nuclide(s) at each designated position. For all other positions, the absence of nuclide(s) indication means that the nuclide(s) composition is the natural one. Related Terms: 1) nuclide (http://doi.org/10.1351/goldbook.N04257). Source: Blue Book, p. 514 (https://www.acdlabs.com/iupac/nomenclature/) Citation: 'isotopically substituted' 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.I03338 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.