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onium compounds

  1. Cations (with their counter-ions) derived by addition of a hydron to a mononuclear parent hydride of the nitrogen, chalcogen and halogen families.
    (H4N+) ammonium
    (H3O+) oxonium
    (H2F+) fluoronium
    (H4P+) phosphonium
    (H3S+) sulfonium
    (H2Cl+) chloronium
    (H4As+) arsonium
    (H3Se+) selenonium
    (H2Br+) bromonium
    (H4Sb+) stibonium
    (H3Te+) telluronium
    (H2I+) iodonium
    (H4Bi+) bismuthonium
  2. Derivatives 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. (Cl2F+) dichlorofluoronium, (CH3)2S+H dimethylsulfonium (a secondary sulfonium ion), Cl(CH3)3P+ chlorotrimethylphosphonium, (CH3CH2)4N+ tetraethylammonium (a quaternary ammonium ion).
    See also: arsonium compounds, halonium ions, oxonium ions, phosphonium compounds, quaternary ammonium compounds, stibonium compounds, sulfonium compounds
  3. Derivatives 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. RC≡O+ hydrocarbylidyne oxonium ions, R2C=N+H2X−iminium compounds, RC≡NH+nitrilium ions.
Source:
PAC, 1995, 67, 1307 (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1353
PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1146
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IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook.
Last update: 2014-02-24; version: 2.3.3.
DOI of this term: https://doi.org/10.1351/goldbook.O04291.
Original PDF version: http://www.iupac.org/goldbook/O04291.pdf. The PDF version is out of date and is provided for reference purposes only. For some entries, the PDF version may be unavailable.
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