onium ion
{{Short description|Class of positively-charged molecules}}
{{Distinguish|text=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, {{chem2|NH4+}}, the protonated derivative of ammonia, {{chem2|NH3}}.
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, {{chem2|(C6H5)4P+}}. The substituent groups may be divalent or trivalent, yielding ions such as iminium and nitrilium.
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 {{nowrap|-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 {{nowrap|-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)
= [[Boron group|Group 13]] (boron group) onium cations =
= [[Carbon group|Group 14]] (carbon group) onium cations =
- carbonium ions (protonated hydrocarbons) have a pentacoordinated carbon atom with a +1 charge.
- alkanium cations, {{chem|C|n|H|2n+3|+}} (protonated alkanes)
- methanium, {{chem2|CH5+}} (protonated methane) (Sometimes called carbonium, because it is the simplest member of that class, but that use is deprecated because of multiple definitions.[https://goldbook.iupac.org/terms/view/C00839 Carbonium ion], IUPAC Gold Book Sometimes called methonium, but methonium also has multiple definitions. Abundant in outer space.)
- ethanium, {{chem2|C2H7+}} (protonated ethane)
- propanium, {{chem2|C3H9+}} (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, {{chem2|C4H11+}} (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)
- octonium or octanium, {{chem2|C8H19+}} (protonated octane)
- silanium (sometimes silonium), {{chem2|SiH5+}} (protonated silane) (should not be called siliconium[https://iupac.qmul.ac.uk/ions/RC821.html RC-82. Cations], Queen Mary University of London)
- disilanium, {{chem2|Si2H7+}} (protonated disilane)
- further silanium cations, {{chem|Si|n|H|2n+3|+}} (protonated silanes)
- germonium, {{chem2|GeH5+}} (protonated germane)
- stannonium, {{chem2|SnH3+}} (protonated {{chem2|SnH2}}) (not protonated stannane {{chem2|SnH4}})
- plumbonium, {{chem2|PbH3+}} (protonated {{chem2|PbH2}}) (not protonated plumbane {{chem2|PbH4}})
- flerovonium, {{chem2|FlH3+}} (protonated {{chem2|FlH2}}) (not protonated flerovane {{chem2|FlH4}})
=[[Pnictogen|Group 15]] (pnictogen) onium cations=
- ammonium (IUPAC name azanium), {{chem2|NH4+}} (protonated ammonia (IUPAC name azane))
- phosphonium, {{chem2|PH4+}} (protonated phosphine)
- arsonium, {{chem2|AsH4+}} (protonated arsine)
- stibonium, {{chem2|SbH4+}} (protonated stibine)
- bismuthonium, {{chem2|BiH4+}} (protonated bismuthine)
- moscovonium, {{chem2|McH4+}} (protonated moscovine)
=[[Chalcogen|Group 16]] (chalcogen) onium cations=
- oxonium, {{chem2|H3O+}} (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, {{chem2|H3S+}} (protonated hydrogen sulfide)
- selenonium, {{chem2|H3Se+}} (protonated hydrogen selenide)
- telluronium, {{chem2|H3Te+}} (protonated hydrogen telluride)
- polononium, {{chem2|H3Po+}} (protonated hydrogen polonide)
- livermoronium, {{chem2|H3Lv+}} (protonated hydrogen livermoride)
=Hydrogen onium cation=
- hydrogenonium, better known as trihydrogen cation, {{chem2|H3+}} (protonated molecular or diatomic hydrogen), found in ionized hydrogen and interstellar space
=[[Halogen|Group 17]] (halogen) onium cations, [[halonium ion]]s, {{chem2|H2X+}} (protonated [[hydrogen halide]]s)=
- fluoronium, {{chem2|H2F+}} (protonated hydrogen fluoride)
- chloronium, {{chem2|H2Cl+}} (protonated hydrogen chloride)
- bromonium, {{chem2|H2Br+}} (protonated hydrogen bromide)
- iodonium, {{chem2|H2I+}} (protonated hydrogen iodide)
- astatonium, {{chem2|H2At+}} (protonated hydrogen astatide)
- tennessonium, {{chem2|H2Ts+}} (protonated hydrogen tennesside)
==[[Pseudohalogen]] onium cations==
- aminodiazonium, {{chem2|[H2N\dN\dN]+ ⇌ [H2N\sN\tN]+}} (protonated hydrogen azide)
- methylidyneammonium and hydrocyanonium, {{chem2|H2CN+}}, isomers {{chem2|HC\tNH+ ⇌ N\tCH2+}} (protonated hydrogen cyanide)
=[[Noble gas|Group 18]] (noble gas) onium cations=
- hydrohelium or helonium, better known as helium hydride ion, {{chem2|HeH+}} (protonated helium)
- neonium, {{chem2|NeH+}} (protonated neon)
- argonium, {{chem2|ArH+}} (protonated argon)
- kryptonium, {{chem2|KrH+}} (protonated krypton)
- xenonium, {{chem2|XeH+}} (protonated xenon)
- radonium, {{chem2|RnH+}} (protonated radon)
- oganessonium {{chem2|OgH+}} (protonated oganesson)
Onium cations with monovalent substitutions
- primary ammonium cations, {{chem2|RH3N+}} or {{chem2|R\sNH3+}} (protonated primary amines)
- hydroxylammonium, {{chem2|H3N+\sOH}} (protonated hydroxylamine)
- methylammonium, {{chem2|CH3NH3+}} (protonated methylamine)
- ethylammonium, {{chem2|CH3CH2NH3+}} (protonated ethylamine)
- hydrazinium, or diazanium, {{chem2|H2N\sNH3+}} (protonated hydrazine, a.k.a. diazane)
- anilinium (a.k.a. phenylammonium), {{chem2|C6H5\sNH3+}} (protonated aniline, a.k.a. phenylamine, aminobenzene)
- secondary ammonium cations, {{chem2|R2NH2+}} (protonated secondary amines)
- dimethylammonium (sometimes dimethylaminium), {{chem2|(CH3)2NH2+}} (protonated dimethylamine)
- diethylammonium (sometimes diethylaminium), {{chem2|(CH3CH2)2NH2+}} (protonated diethylamine)
- ethylmethylammonium, {{chem2|(CH3CH2)(CH3)NH2+}} (protonated ethylmethylamine)
- diethanolammonium (sometimes diethanolaminium), {{chem2|(OHCH2CH2)2NH2+}} (protonated diethanolamine)
- tertiary ammonium cations, {{chem2|R3NH+}} (protonated tertiary amines)
- trimethylammonium {{chem2|(CH3)3NH+}} (protonated trimethylamine)
- triethylammonium {{chem2|(CH3CH2)3NH+}} (protonated triethylamine)
- quaternary ammonium cations, {{chem2|R4N+}} or {{chem2|NR4+}}
- tetrafluoroammonium, {{chem2|NF4+}}
- tetramethylammonium, {{chem2|(CH3)4N+}}
- tetraethylammonium, {{chem2|(CH3CH2)4N+}}
- tetrapropylammonium, {{chem2|(CH3(CH2)2)4N+}}
- tetrabutylammonium, {{chem2|(CH3(CH2)3)4N+}} or abbreviated {{chem2|Bu4N+}}
- trimethyl ammonium compounds, {{chem2|(CH3)3RN+}}
- didecyldimethylammonium, {{chem2|(CH3(CH2)9)2(CH3)2N+}}
- pentamethylhydrazinium, {{chem2|(CH3)2N\sN(CH3)3+}}
- quaternary phosphonium cations, {{chem2|R4P+}} or {{chem2|PR4+}}
- tetraphenylphosphonium, {{chem2|(C6H5)4P+}}
- quaternary arsonium cations, {{chem2|R4As+}} or {{chem2|AsR4+}}
- tetraphenylarsonium, {{chem2|(C6H5)4As+}}
- quaternary stibonium cations, {{chem2|R4Sb+}} or {{chem2|SbR4+}}
- tetraphenylstibonium, {{chem2|(C6H5)4Sb+}}
- primary oxonium cations, {{chem2|ROH2+}} (protonated alcohols {{chem2|R\sO\sH}})
- alkyloxonium cations {{chem2|ROH2+}} (protonated alcohols)
- methyloxonium, {{chem2|CH3OH2+}} (protonated methanol)
- ethyloxonium, {{chem2|CH3CH2OH2+}} (protonated ethanol)
- dioxidanonium (hydroxylhydronium), {{chem2|HO\sOH2+}} (protonated hydrogen peroxide)
- secondary oxonium cations, {{chem2|R2OH+}} (protonated ethers {{chem2|R\sO\sR}})
- dialkyloxonium cations (protonated ethers)
- dimethyloxonium, {{chem2|(CH3)2OH+}} (protonated dimethyl ether)
- tertiary oxonium cations, {{chem2|R3O+}}
- trifluorooxonium, {{chem2|OF3+}} (hypothetical)
- trimethyloxonium, {{chem2|(CH3)3O+}}
- triethyloxonium, {{chem2|(CH3CH2)3O+}}
- oxatriquinacene, {{chem2|C9H9O+}} (cyclic oxonium ion)
- oxatriquinane, {{chem2|C9H15O+}} (cyclic oxonium ion)
- primary sulfonium cations, {{chem2|RSH2+}} (protonated thiols {{chem2|R\sS\sH}})
- secondary sulfonium cations, {{chem2|R2SH+}} (protonated thioethers {{chem2|R\sS\sR}})
- dimethylsulfonium, {{chem2|(CH3)2SH+}} (protonated dimethyl sulfide)
- tertiary sulfonium cations, {{chem2|R3S+}}
- trimethylsulfonium, {{chem2|(CH3)3S+}}
- tertiary selenonium cations, {{chem2|R3Se+}}
- triphenylselenonium, {{chem2|(C6H5)3Se+}}
- tertiary telluronium cations, {{chem2|R3Te+}}
- triphenyltelluronium, {{chem2|(C6H5)3Te+}}
- primary fluoronium cations, {{chem2|RFH+}} (protonated fluorides RF)
- secondary fluoronium cations, {{chem2|R2F+}}
- dichlorofluoronium, {{chem2|Cl2F+}}
- secondary iodonium cations, {{chem2|R2I+}}
- diphenyliodonium, {{chem2|(C6H5)2I+}}
Onium cations with polyvalent substitutions
- secondary ammonium cations having one double-bonded substitution, {{chem2|R\dNH2+}}
- diazenium, {{chem2|HN\dNH2+}} (protonated diazene)
- guanidinium, {{chem2|C(NH2)3+}} (protonated guanidine) (has a resonance structure and a planar molecular geometry)
- tertiary ammonium cations having one triple-bonded substitution, R≡NH+
- nitrilium, {{chem2|R\sC\tNH+}} (protonated nitrile)
- diazonium or diazynium, {{chem2|N\tNH+}} (protonated nitrogen, in other words, protonated diazyne)
- cyclic tertiary ammonium cations where nitrogen is a member of a ring, {{chem2|RNH+R}} (the ring may be aromatic)
- pyridinium, {{chem2|C5H5NH+}} (protonated pyridine)
- quaternary ammonium cations having one double-bonded substitution and two single-bonded substitutions, {{chem2|R\dNR2+}}
- iminium, {{chem2|R2C\dNR2+}} (substituted protonated imine)
- diazenium, {{chem2|RN\dNR2+}} (substituted protonated diazene)
- thiazolium, {{chem2|[C3NSR4]+}}(substituted protonated thiazole)
- quaternary ammonium cations having two double-bonded substitutions, {{chem2|R\dN+\dR}}
- nitronium, {{chem2|[NO2]+}}
- bis(triphenylphosphine)iminium, {{chem2|((C6H5)3P\d)2N+}}
- quaternary ammonium cations having one triple-bonded substitution and one single-bonded substitution, {{chem2|R\tNR+}}
- diazonium, {{chem2|N\tNR+}} (substituted protonated nitrogen, in other words, substituted protonated diazyne)
- nitrilium, {{chem2|RC\tNR+}} (substituted protonated nitrile)
- tertiary oxonium cations having one triple-bonded substitution, {{chem2|R\tO+}}
- acylium ions, {{chem2|R\sC\tO+ ↔ R\sC+\dO}}
- nitrosonium, {{chem2|N\tO+}}
- cyclic tertiary oxonium cations where oxygen is a member of a ring, {{chem2|RO+R}} (the ring may be aromatic)
- pyrylium, {{chem2|C5H5O+}}
- tertiary sulfonium cations having one triple-bonded substitution, {{chem2|R\tS+}}
- thionitrosyl, {{chem2|N\tS+}}
- dihydroxyoxoammonium, {{chem2|[H2NO3]+}} (protonated nitric acid)
- trihydroxyoxosulfonium, {{chem2|[H3SO4]+}} (protonated sulfuric acid)
Double onium dications
- hydrazinediium or hydrazinium(2+) dication, {{chem2|H3N+\s+NH3}} (doubly protonated hydrazine, in other words, doubly protonated diazane)
- diazenediium cation, {{chem2|H2N+\d+NH2}} (doubly protonated diazene)
- diazynediium cation, {{chem2|HN+\t+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, {{chem2|R2B+}} (protonated borylenes a.k.a. boranylidenes)
- carbenium cations, {{chem2|R3C+}} (protonated carbenes) have a tricoordinated carbon atom with a +1 charge.
- alkenium cations, {{chem|C|n|H|2n+1|+}} (n ≥ 2) (protonated alkenes)
- methenium cation, {{chem2|H3C+}} (protonated methylene)
- ethenium, {{chem2|C2H5+}} (protonated ethene)
- benzenium, {{chem2|C6H7+}} (protonated benzene)
- tropylium, {{chem2|C7H7+}} (protonated tropylidene)
- silylium cations, {{chem2|R3Si+}} (protonated silylenes)
- nitrenium cations, {{chem2|R2N+}} (protonated nitrenes)
- phosphinidenium cations, {{chem2|R2P+}} (protonated phosphinidene)
- mercurinium cations, {{chem2|R3Hg+}} (protonated organomercury compounds; formed as intermediates in oxymercuration reactions)
=Substituted eniums=
- diphenylcarbenium, {{chem2|(C6H5)2CH+}} (di-substituted methenium)
- triphenylcarbenium, {{chem2|(C6H5)3C+}} (tri-substituted methenium)
Ynium cations
- carbynium ions (protonated carbynes) have a carbon atom with a +1 charge.
- alkynium cations, {{chem|C|n|H|2n-1|+}} (n ≥ 2) (protonated alkynes)
- methynium cation, {{chem2|H2C+}} (protonated methylidyne radical)
- ethynium, {{chem2|C2H3+}} (protonated ethyne)
See also
- Carbonium ion
- Lyonium ion, a protonated solvent molecule
- Lyate ion, a deprotonated solvent molecule
References
External links
- [https://iupac.qmul.ac.uk/class/ionra.html#36 Ions and Radicals], Queen Mary University of London
- {{MeSH name|Onium compounds}}
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