12561 IUPAC Gold Book - ring and double bond equivalent 10.1351/goldbook.12561 12561 current 1 Conventional measure of the degree of unsaturation of an organic molecule given by \(X - Y/2 + Z/2 + 1\) where \(X\) is the number of carbon atoms, \(Y\) is the number of hydrogen or halogen atoms and \(Z\) is the number of nitrogen and phosphorus atoms. PAC, 2013, 85, 1515. 'Definitions of terms relating to mass spectrometry (IUPAC Recommendations 2013)' on page 1588 (https://doi.org/10.1351/PAC-REC-06-04-06) https://goldbook.iupac.org/terms/view/12561/html https://goldbook.iupac.org/terms/view/12561/json https://goldbook.iupac.org/terms/view/12561/plain Citation: 'ring and double bond equivalent' 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.12561 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. 2026-04-17T23:45:12+00:00