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In chemistry, an onium compound, or onium ion, is a cation formally obtained by the protonation of mononuclear parent hydride of a pnictogen (group 15 of the periodic table), chalcogen (group 16), or halogen (group 17). The oldest-known onium ion, and the namesake for the class, is ammonium, , the protonated derivative of ammonia, .〔〔 The name onium is also used for cations that would result from the substitution of hydrogen atoms in those ions by other groups, such as organic radicals, or halogens; such as tetraphenylphosphonium, . The substituent groups may be di- or trivalent, yielding ions such as iminium and nitrilium.〔(IUPAC definition )〕〔 Onium ions have a charge of +1. A molecule with two or more onium ion subgroups is said to be a double onium ion, triple onium ion, and so on. Compounds of an onium cation and some other negative ion are known as onium salts. Onium compounds are inversely analogous to ate complexes. Lewis bases form onium ions when the central atom gains one more bond and becomes a positive cation. Lewis acids form -ate ions when the central atom gains one more bond and becomes a negative anion. 〔''Advanced Organic Chemistry: Reactions and mechanisms'', Maya Shankar Singh, 2007, Dorling Kindersley, ISBN 978-81-317-1107-1〕 ==Simple onium cations (hydrides with no substitutions)== ===Group 15 (pnictogen) onium cations=== *ammonium (IUPAC name azanium), (protonated ammonia (IUPAC name azane)) *phosphonium, (protonated phosphine) *arsonium, (protonated arsine) *stibonium, (protonated stibine) *bismuthonium, (protonated bismuthine) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「onium compound」の詳細全文を読む スポンサード リンク
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