Chemistry:Onium ion
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, NH
3.[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, (C
6H
5)
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]
Simple onium cations (hydrides with no substitutions)
Group 13 (boron group) onium cations
Group 14 (carbon group) onium cations
- carbonium ions (protonated hydrocarbons) have a pentacoordinated carbon atom with a +1 charge.
- alkanium cations, CnH+2n+3 (protonated alkanes)
- methanium, CH+
5 (protonated methane) (Sometimes called carbonium, because it is the simplest member of that class, but that use is deprecated because of multiple definitions.[4] Sometimes called methonium, but methonium also has multiple definitions. Abundant in outer space.) - ethanium, C
2H+
7 (protonated ethane) - propanium, C
3H+
9 (propane protonated on an unspecified carbon)- propylium, or propan-1-ylium (propane protonated on an end carbon)
- propan-2-ylium (propane protonated on the middle carbon)
- butanium, C
4H+
11 (butane protonated on an unspecified carbon)- n-butanium (n-butane protonated on an unspecified carbon)
- n-butylium, or n-butan-1-ylium (n-butane protonated on an end carbon)
- n-butan-2-ylium (n-butane protonated on a middle carbon)
- isobutanium (isobutane protonated on an unspecified carbon)
- isobutylium, or isobutan-1-ylium (isobutane protonated on an end carbon)
- isobutan-2-ylium (isobutane protonated on the middle carbon)
- n-butanium (n-butane protonated on an unspecified carbon)
- octonium or octanium, C
8H+
19 (protonated octane)
- methanium, CH+
- alkanium cations, CnH+2n+3 (protonated alkanes)
- silanium (sometimes silonium), SiH+
5 (protonated silane) (should not be called siliconium[5] - germonium, GeH+
5 (protonated germane) - stannonium, SnH+
3 (protonated SnH
2) (not protonated stannane SnH
4) - plumbonium, PbH+
3 (protonated PbH
2) (not protonated plumbane PbH
4) - flerovonium, FlH+
3 (protonated FlH
2) (not protonated flerovane FlH
4)
Group 15 (pnictogen) onium cations
- ammonium (IUPAC name azanium), NH+
4 (protonated ammonia (IUPAC name azane)) - phosphonium, PH+
4 (protonated phosphine) - arsonium, AsH+
4 (protonated arsine) - stibonium, SbH+
4 (protonated stibine) - bismuthonium, BiH+
4 (protonated bismuthine) - moscovonium, McH+
4 (protonated moscovine)
Group 16 (chalcogen) onium cations
- oxonium, H
3O+
(protonated water (IUPAC name oxidane). Oxonium is better known as hydronium, though hydronium implies a solvated or hydrated proton. It may also be called hydroxonium.) - sulfonium, H
3S+
(protonated hydrogen sulfide) - selenonium, H
3Se+
(protonated hydrogen selenide) - telluronium, H
3Te+
(protonated hydrogen telluride) - polononium, H
3Po+
(protonated hydrogen polonide) - livermoronium, H
3Lv+
(protonated hydrogen livermoride)
Hydrogen onium cation
- hydrogenonium, better known as trihydrogen cation, H+
3 (protonated molecular or diatomic hydrogen), found in ionized hydrogen and interstellar space
Group 17 (halogen) onium cations, halonium ions, H
2X+
(protonated hydrogen halides)
- fluoronium, H
2F+
(protonated hydrogen fluoride) - chloronium, H
2Cl+
(protonated hydrogen chloride) - bromonium, H
2Br+
(protonated hydrogen bromide) - iodonium, H
2I+
(protonated hydrogen iodide) - astatonium, H
2At+
(protonated hydrogen astatide) - tennessonium, H
2Ts+
(protonated hydrogen tennesside)
Pseudohalogen onium cations
- aminodiazonium, [H
2N=N=N]+
⇌ [H
2N–N≡N]+
(protonated hydrogen azide) - methylidyneammonium and hydrocyanonium, H
2CN+
, isomers HC≡NH+
⇌ N≡CH+
2 (protonated hydrogen cyanide)
Group 18 (noble gas) onium cations
- hydrohelium or helonium, better known as helium hydride ion, HeH+
(protonated helium) - neonium, NeH+
(protonated neon) - argonium, ArH+
(protonated argon) - kryptonium, KrH+
(protonated krypton) - xenonium, XeH+
(protonated xenon) - radonium, RnH+
(protonated radon) - oganessonium OgH+
(protonated oganesson)
Onium cations with monovalent substitutions
- primary ammonium cations, RH
3N+
or R–NH+
3 (protonated primary amines)- hydroxylammonium, H
3N+
–OH (protonated hydroxylamine) - methylammonium, CH
3NH+
3 (protonated methylamine) - ethylammonium, CH
3CH
2NH+
3 (protonated ethylamine) - hydrazinium, or diazanium, H
2N–NH+
3 (protonated hydrazine, a.k.a. diazane) - anilinium (a.k.a. phenylammonium), C
6H
5–NH+
3 (protonated aniline, a.k.a. phenylamine, aminobenzene)
- hydroxylammonium, H
- secondary ammonium cations, R
2NH+
2 (protonated secondary amines)- dimethylammonium (sometimes dimethylaminium), (CH
3)
2NH+
2 (protonated dimethylamine) - diethylammonium (sometimes diethylaminium), (CH
3CH
2)
2NH+
2 (protonated diethylamine) - ethylmethylammonium, (CH
3CH
2)(CH
3)NH+
2 (protonated ethylmethylamine) - diethanolammonium (sometimes diethanolaminium), (OHCH
2CH
2)
2NH+
2 (protonated diethanolamine)
- dimethylammonium (sometimes dimethylaminium), (CH
- tertiary ammonium cations, R
3NH+
(protonated tertiary amines)- trimethylammonium (CH
3)
3NH+
(protonated trimethylamine) - triethylammonium (CH
3CH
2)
3NH+
(protonated triethylamine)
- trimethylammonium (CH
- quaternary ammonium cations, R
4N+
or NR+
4- tetrafluoroammonium, NF+
4 - tetramethylammonium, (CH
3)
4N+ - tetraethylammonium, (CH
3CH
2)
4N+ - tetrapropylammonium, (CH
3(CH
2)
2)
4N+ - tetrabutylammonium, (CH
3(CH
2)
3)
4N+
or abbreviated Bu
4N+ - trimethyl ammonium compounds, (CH
3)
3RN+ - didecyldimethylammonium, (CH
3(CH
2)
9)
2(CH
3)
2N+ - pentamethylhydrazinium, (CH
3)
2N–N(CH
3)+
3
- tetrafluoroammonium, NF+
- quaternary phosphonium cations, R
4P+
or PR+
4- tetraphenylphosphonium, (C
6H
5)
4P+
- tetraphenylphosphonium, (C
- quaternary arsonium cations, R
4As+
or AsR+
4- tetraphenylarsonium, (C
6H
5)
4As+
- tetraphenylarsonium, (C
- quaternary stibonium cations, R
4Sb+
or SbR+
4- tetraphenylstibonium, (C
6H
5)
4Sb+
- tetraphenylstibonium, (C
- primary oxonium cations, ROH+
2 (protonated alcohols R–O–H)- alkyloxonium cations ROH+
2 (protonated alcohols) - dioxidanonium (hydroxylhydronium), HO–OH+
2 (protonated hydrogen peroxide)
- alkyloxonium cations ROH+
- secondary oxonium cations, R
2OH+
(protonated ethers R–O–R)- dialkyloxonium cations (protonated ethers)
- dimethyloxonium, (CH
3)
2OH+
(protonated dimethyl ether)
- dimethyloxonium, (CH
- dialkyloxonium cations (protonated ethers)
- tertiary oxonium cations, R
3O+
- trifluorooxonium, OF+
3 (hypothetical) - trimethyloxonium, (CH
3)
3O+ - triethyloxonium, (CH
3CH
2)
3O+ - oxatriquinacene, C
9H
9O+
(cyclic oxonium ion) - oxatriquinane, C
9H
15O+
(cyclic oxonium ion)
- trifluorooxonium, OF+
- primary sulfonium cations, RSH+
2 (protonated thiols R–S–H) - secondary sulfonium cations, R
2SH+
(protonated thioethers R–S–R)- dimethylsulfonium, (CH
3)
2SH+
(protonated dimethyl sulfide)
- dimethylsulfonium, (CH
- tertiary sulfonium cations, R
3S+
- trimethylsulfonium, (CH
3)
3S+
- trimethylsulfonium, (CH
- tertiary selenonium cations, R
3Se+
- triphenylselenonium, (C
6H
5)
3Se+
- triphenylselenonium, (C
- tertiary telluronium cations, R
3Te+
- triphenyltelluronium, (C
6H
5)
3Te+
- triphenyltelluronium, (C
- primary fluoronium cations, RFH+
(protonated fluorides RF) - secondary fluoronium cations, R
2F+
- dichlorofluoronium, Cl
2F+
- dichlorofluoronium, Cl
- secondary iodonium cations, R
2I+
- diphenyliodonium, (C
6H
5)
2I+
- diphenyliodonium, (C
Onium cations with polyvalent substitutions
- secondary ammonium cations having one double-bonded substitution, R=NH+
2 - tertiary ammonium cations having one triple-bonded substitution, R≡NH+
- cyclic tertiary ammonium cations where nitrogen is a member of a ring, RNH+
R (the ring may be aromatic)- pyridinium, C
5H
5NH+
(protonated pyridine)
- pyridinium, C
- quaternary ammonium cations having one double-bonded substitution and two single-bonded substitutions, R=NR+
2 - quaternary ammonium cations having two double-bonded substitutions, R=N+
=R- nitronium, [NO
2]+ - bis(triphenylphosphine)iminium, ((C
6H
5)
3P=)
2N+
- nitronium, [NO
- quaternary ammonium cations having one triple-bonded substitution and one single-bonded substitution, R≡NR+
- diazonium, N≡NR+
(substituted protonated nitrogen, in other words, substituted protonated diazyne) - nitrilium, RC≡NR+
(substituted protonated nitrile)
- diazonium, N≡NR+
- tertiary oxonium cations having one triple-bonded substitution, R≡O+
- acylium ions, R–C≡O+
↔ R–C+
=O - nitrosonium, N≡O+
- acylium ions, R–C≡O+
- cyclic tertiary oxonium cations where oxygen is a member of a ring, RO+
R (the ring may be aromatic)- pyrylium, C
5H
5O+
- pyrylium, C
- tertiary sulfonium cations having one triple-bonded substitution, R≡S+
- thionitrosyl, N≡S+
- thionitrosyl, N≡S+
- dihydroxyoxoammonium, [H
2NO
3]+
(protonated nitric acid) - trihydroxyoxosulfonium, [H
3SO
4]+
(protonated sulfuric acid)
Double onium dications
- hydrazinediium or hydrazinium(2+) dication, H
3N+
–+
NH
3 (doubly protonated hydrazine, in other words, doubly protonated diazane) - diazenediium cation, H
2N+
=+
NH
2 (doubly protonated diazene) - diazynediium cation, HN+
≡+
NH (doubly protonated dinitrogen, in other words, doubly protonated diazyne)
Enium cations
The extra bond is added to a less-common parent hydride, a carbene analog, typically named -ene or -ylene, which is neutral with 2 fewer bonds than the more-common hydride, typically named -ane or -ine.
- borenium cations, R
2B+
(protonated borylenes a.k.a. boranylidenes) - carbenium cations, R
3C+
(protonated carbenes) have a tricoordinated carbon atom with a +1 charge. - silylium cations, R
3Si+
(protonated silylenes) - nitrenium cations, R
2N+
(protonated nitrenes) - phosphinidenium cations, R
2P+
(protonated phosphinidene) - mercurinium cations, R
3Hg+
(protonated organomercury compounds; formed as intermediates in oxymercuration reactions)
Substituted eniums
- diphenylcarbenium, (C
6H
5)
2CH+
(di-substituted methenium) - triphenylcarbenium, (C
6H
5)
3C+
(tri-substituted methenium)
Ynium cations
- carbynium ions (protonated carbynes) have a carbon atom with a +1 charge.
- alkynium cations, CnH+2n-1 (n ≥ 2) (protonated alkynes)
- methynium cation, H
2C+
(protonated methylidyne radical) - ethynium, C
2H+
3 (protonated ethyne)
- methynium cation, H
- alkynium cations, CnH+2n-1 (n ≥ 2) (protonated alkynes)
See also
- Carbonium ion
- Lyonium ion, a protonated solvent molecule
- Lyate ion, a deprotonated solvent molecule
References
- ↑ Jump up to: 1.0 1.1 Onium compounds, IUPAC Gold Book
- ↑ Jump up to: 2.0 2.1 George A. Olah (1998). Onium Ions. John Wiley & Sons. pp. 509. ISBN 9780471148777.
- ↑ Advanced Organic Chemistry: Reactions and mechanisms, Maya Shankar Singh, 2007, Dorling Kindersley, ISBN:978-81-317-1107-1
- ↑ Carbonium ion, IUPAC Gold Book
- ↑ RC-82. Cations, Queen Mary University of London)
External links
- Ions and Radicals, Queen Mary University of London
- Onium compounds at the US National Library of Medicine Medical Subject Headings (MeSH)
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