Not to be confused with onium states such as positronium.
In chemistry, an 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, NH+4, the protonated derivative of ammonia, NH3.[1][2]
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 groups, or halogens; such as tetraphenylphosphonium, (C6H5)4P+. The substituent groups may be divalent or trivalent, yielding ions such as iminium and nitrilium.[1][2]
A simple onium ion has a charge of +1. A larger ion that has two onium ion subgroups is called a double onium ion, and has a charge of +2. A triple onium ion has a charge of +3, and so on.
Compounds of an onium cation and some other anion are known as onium compounds or onium salts.
Onium ions and onium compounds are inversely analogous to -ate ions and 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.[3]
^ abCite error: The named reference IUPAC was invoked but never defined (see the help page).
^ abCite error: The named reference OlahBk was invoked but never defined (see the help page).
^Advanced Organic Chemistry: Reactions and mechanisms, Maya Shankar Singh, 2007, Dorling Kindersley, ISBN 978-81-317-1107-1
triple oniumion has a charge of +3, and so on. Compounds of an onium cation and some other anion are known as onium compounds or onium salts. Oniumions and...
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given, as the number of polyatomic ions encountered in practice is very large. Monatomic ion Protonation Oniumion Petrucci, Ralph H.; Herring, F. Geoffrey;...
An onium (plural: onia) is a bound state of a particle and its antiparticle. These states are usually named by adding the suffix -onium to the name of...
molecules More carbonium ions called non-classical ions are found in certain norbornyl systems Onium compounds Carbenium ion George Andrew Olah (1972)...
C8H8N+, and forms chemical compounds in combination with anions. It is an oniumion derived from its parent compound, indole, by the addition of a proton...
kryptonium ion, KrH+, is an oniumion, consisting of protonated krypton. Kryptonium is known in dilute gas phase. Although salts of the fluorokryptonium ion, KrF+...
of protolytic solvents. Lyate ion, a deprotonated solvent molecule Oniumion, a protonated molecule more generally Ion transport number Ionic atmosphere...
atom, such as a quaternary ammonium or phosphonium cation (generally: oniumions), and with a negatively charged functional group, such as a carboxylate...
+1 electric charge. It is a superacid and one of the oniumions, indeed the simplest carbonium ion. It is highly unstable and highly reactive even upon...
higher oxidation states. Ate complexes are a counterpart to oniumions. Lewis acids form ate ions when the central atom reacts with a donor (2 e− X-type ligand)...
counter ion. It is thought that the acidic proton generated is what ultimately initiates the polymerization. Since their discovery in the 1970s aryl onium salts...
purple Ph5Bi was the first to be synthesized so. Bi(V) easily forms an oniumion for example by protonation with p-toluenesulfonic acid: Ph5Bi + HO3SAr...
perchlorate. The proposed reaction pathway includes oniumion formation with the following perchlorate ion addition. The “doping effect” can also be observed...
electrophilic attack of H+ or R+ on an alkane, in analogy to other main group onium species, while a carbocation that contains any type of three-centered bonding...
The ammonium cation is a positively charged polyatomic ion with the chemical formula NH+4 or [NH4]+. It is formed by the protonation of ammonia (NH3)...
In organic chemistry, a sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively-charged ion (a "cation") featuring three organic...
known as mustards.[citation needed] Such compounds can form cyclic "onium" ions (sulfonium, ammonium, etc.) that are good alkylating agents. Other such...
George A.; Donovan, Daniel J.; Shen, Jacob; Klopman, Gilles (1975). "Oniumions. XVI. Hydrogen-deuterium exchange accompanying the cleavage of ammonium...
characteristics of molten salts derived from trimethylsulfonium bromide". Canadian Journal of Chemistry. 73 (4): 593–598. doi:10.1139/v95-076. Onium compounds...
The xenonium ion, XeH+, is an onium compound, consisting of protonated xenon. Although the existence of the xenonium salts has not been proven, the isolated...
"Onium Ylide chemistry. 1. Bifunctional acid-base-catalyzed conversion of heterosubstituted methanes into ethylene and derived hydrocarbons. The onium...
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