Term: carbenium ion https://doi.org/10.1351/goldbook.C00812 Definition: A generic name for carbocations, real or hypothetical, that have at least one important contributing structure containing a tervalent carbon atom with a vacant p-orbital. (The name implies a protonated carbene or a substitution derivative thereof.) The term was proposed (and rejected) as a replacement for the traditional usage of the name carbonium ion. To avoid ambiguity, the name should not be used as the root for the systematic nomenclature of carbocations. The corresponding difficulty confused carbonium ion nomenclature for many years. For example, the term 'ethylcarbonium ion' has at times been used to refer either to CH3CH2+ (ethyl cation) or (correctly) to CH3CH2CH2+ (propyl cation). Related Terms: 1) carbocations (http://doi.org/10.1351/goldbook.C00817). 2) contributing structure (http://doi.org/10.1351/goldbook.C01309). 3) carbonium ion (http://doi.org/10.1351/goldbook.C00839). 4) cation (http://doi.org/10.1351/goldbook.C00907). Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1092 (https://doi.org/10.1351/pac199466051077) Citation: 'carbenium ion' 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.C00812 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.