{"term":{"id":"04291","title":"onium compounds","longtitle":"IUPAC Gold Book - onium compounds","doi":"10.1351\/goldbook.O04291","code":"O04291","status":"current","definitions":[{"id":1,"text":"Cations (with their counter-ions) derived by addition of a hydron to a mononuclear parent hydride of the nitrogen, chalcogen and halogen families.$\\ce{H4N^{+}}$ ammonium$\\ce{H3O^{+}}$ oxonium$\\ce{H2F^{+}}$ fluoronium$\\ce{H4P^{+}}$ phosphonium$\\ce{H3S^{+}}$ sulfonium$\\ce{H2Cl^{+}}$ chloronium$\\ce{H4As^{+}}$ arsonium$\\ce{H3Se^{+}}$ selenonium$\\ce{H2Br^{+}}$ bromonium$\\ce{H4Sb^{+}}$ stibonium$\\ce{H3Te^{+}}$ telluronium$\\ce{H2I^{+}}$ iodonium$\\ce{H4Bi^{+}}$ bismuthoniumDerivatives formed by substitution of the above parent ions by univalent groups. The number of substituted hydrogen atoms is, especially in the case of hydrocarbyl substituents, indicated by the adjectives primary, secondary, tertiary or quaternary. E.g. ($\\ce{Cl2F^{+}}$) dichlorofluoronium, $\\ce{(CH3)2S^{+}H}$ dimethylsulfonium (a secondary sulfonium ion), $\\ce{Cl(CH3)3P^{+}}$ chlorotrimethylphosphonium, $\\ce{(CH3CH2)4N^{+}}$ tetraethylammonium (a quaternary ammonium ion).See also: arsonium compounds, halonium ions, oxonium ions, phosphonium compounds, quaternary ammonium compounds, stibonium compounds, sulfonium compoundsDerivatives formed by substitution of the above parent ions by groups having two or three free valencies on the same atom. Such derivatives are, where possible, designated by a specific class name. E.g. $\\ce{RC#O^{+}}$ hydrocarbylidyne oxonium ions, $\\ce{R2C=N^{+}H2X^{−}}$ iminium compounds, $\\ce{RC#NH^{+}}$ nitrilium ions.","links":[{"term":"Cations","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/C00907"},{"term":"arsonium compounds","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/A00457"},{"term":"counter-ions","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/C01371"},{"term":"halonium ions","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/H02728"},{"term":"hydrocarbyl","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/H02891"},{"term":"hydron","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/H02904"},{"term":"iminium compounds","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/I02958"},{"term":"nitrilium ions","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/N04156"},{"term":"oxonium ions","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/O04378"},{"term":"parent hydride","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/P04405"},{"term":"phosphonium compounds","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/P04562"},{"term":"quaternary ammonium compounds","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/Q05003"},{"term":"stibonium compounds","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/S06011"},{"term":"sulfonium compounds","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/S06121"}],"sources":["PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1146 (https:\/\/doi.org\/10.1351\/pac199466051077)","PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1353 (https:\/\/doi.org\/10.1351\/pac199567081307)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/O04291\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/O04291\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/O04291\/plain"},"citation":"Citation: 'onium compounds' 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.O04291","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.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","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.","accessed":"2026-04-28T20:28:43+00:00"}}