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In
chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
, an onium ion is a
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
formally obtained by the
protonation In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), (H+) to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brønsted–Lowry acid ...
of mononuclear parent
hydride In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride ...
of a pnictogen (group 15 of the
periodic table The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...
),
chalcogen The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioac ...
(group 16), or
halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this grou ...
(group 17). The oldest-known onium ion, and the namesake for the class, is
ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaterna ...
, , the protonated derivative of
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
, . 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 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 An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
are known as onium compounds or onium salts. Onium ions and onium compounds are inversely analogous to ions and ate complexes: *
Lewis bases A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any spe ...
form onium ions when the central atom gains one more bond and becomes a positive
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
. *Lewis acids form ions when the central atom gains one more bond and becomes a negative
anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
.


Simple onium cations (hydrides with no substitutions)


Group 13 The Group 13 network ( pl, Trzynastka, Yiddish: ''דאָס דרײַצענטל'') was a Jewish Nazi collaborationist organization in the Warsaw Ghetto during the German occupation of Poland in World War II. The rise and fall of the Group ...
(boron group) onium cations

*
boronium In chemistry, a boranylium ion is an inorganic cation with the chemical formula , where R represents a non-specific substituent. Being electron-deficient, boranylium ions form adducts with Lewis bases. Boranylium ions have historical names that ...
cation, (protonated borane) **further boronium cations, (protonated boranes)


Group 14 (carbon group) onium cations

*
carbonium ion In chemistry, a carbonium ion is any cation that has a pentavalent carbon atom. The name carbonium may also be used for the simplest member of the class, properly called methanium (), where the five valences are filled with hydrogen atoms. The ...
s (protonated
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s) have a pentavalent carbon atom with a +1 charge. **alkanium cations, (protonated
alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in wh ...
s) ***
methanium In chemistry, methanium is a complex positive ion with formula []+, namely a molecule with one carbon atom covalent bond, bonded to three hydrogen atoms and one hydrogen molecule, bearing a +1 electric charge. It is a superacid and one of the ...
, (protonated
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
) (Sometimes called
carbonium In chemistry, a carbonium ion is any cation that has a pentavalent carbon atom. The name carbonium may also be used for the simplest member of the class, properly called methanium (), where the five valences are filled with hydrogen atoms. The ...
, because it is the simplest member of that class, but that use is deprecated because of multiple definitions. Sometimes called methonium, but methonium also has multiple definitions. Abundant in outer space.) ***
ethanium In chemistry, ethanium or protonated ethane is a highly reactive positive ion with formula . It can be described as a molecule of ethane () with one extra proton ( hydrogen nucleus), that gives it a +1 electric charge. Ethanium is one of th ...
, (protonated
ethane Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...
) *** propanium, (
propane Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as ...
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, (
butane Butane () or ''n''-butane is an alkane with the formula C4H10. Butane is a gas at room temperature and atmospheric pressure. Butane is a highly flammable, colorless, easily liquefied gas that quickly vaporizes at room temperature. The name but ...
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 Isobutane, also known as ''i''-butane, 2-methylpropane or methylpropane, is a chemical compound with molecular formula HC(CH3)3. It is an isomer of butane. Isobutane is a colourless, odourless gas. It is the simplest alkane with a tertiary carbo ...
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 In chemistry, a carbonium ion is any cation that has a pentavalent carbon atom. The name carbonium may also be used for the simplest member of the class, properly called methanium (), where the five valences are filled with hydrogen atoms. The ne ...
or octanium, (protonated
octane Octane is a hydrocarbon and an alkane with the chemical formula , and the condensed structural formula . Octane has many structural isomers that differ by the amount and location of branching in the carbon chain. One of these isomers, 2,2,4-t ...
) * silanium (sometimes silonium), (protonated
silane Silane is an inorganic compound with chemical formula, . It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Sila ...
) (should not be called siliconiumRC-82. Cations
Queen Mary University of London) ** disilanium, (protonated disilane) **further silanium cations, (protonated silanes) * germonium, (protonated
germane Germane is the chemical compound with the formula Ge H4, and the germanium analogue of methane. It is the simplest germanium hydride and one of the most useful compounds of germanium. Like the related compounds silane and methane, germane is ...
) * stannonium, (protonated ) (not protonated stannane ) * plumbonium, (protonated )


Group 15 (pnictogen) onium cations

*
ammonium The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaterna ...
(
IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
name azanium), (protonated
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
(IUPAC name azane)) *
phosphonium In polyatomic cations with the chemical formula (where R is a hydrogen or an alkyl, aryl, or halide group). These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions. Types of phosphonium ...
, (protonated
phosphine Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
) *
arsonium The arsonium cation is a positively charged polyatomic ion with the chemical formula . An arsonium salt is a salt containing either the arsonium () cation, such as arsonium bromide () and arsonium iodide (), which can be synthesized by reacting ...
, (protonated
arsine Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications ...
) * stibonium, (protonated
stibine Stibine (IUPAC name: stibane) is a chemical compound with the formula SbH3. A pnictogen hydride, this colourless, highly toxic gas is the principal covalent hydride of antimony, and a heavy analogue of ammonia. The molecule is pyramidal with H� ...
) * bismuthonium, (protonated
bismuthine Bismuthine (IUPAC name: bismuthane) is the chemical compound with the formula BiH3. As the heaviest analogue of ammonia (a pnictogen hydride), BiH3 is unstable, decomposing to bismuth metal well below 0 °C. This compound adopts the expecte ...
)


Group 16 (chalcogen) onium cations

* oxonium, (protonated
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
(IUPAC name oxidane). Oxonium is better known as
hydronium In chemistry, hydronium (hydroxonium in traditional British English) is the common name for the aqueous cation , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid ...
, though hydronium implies a solvated or hydrated proton. It may also be called hydroxonium.) *
sulfonium In organic chemistry, a sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively-charged ion (a "cation") featuring three organic substituents attached to sulfur. These organosulfur compounds have the formula . Together wi ...
, (protonated
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
) * selenonium, (protonated
hydrogen selenide Hydrogen selenide is an inorganic compound with the formula H2Se. This hydrogen chalcogenide is the simplest and most commonly encountered hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic sel ...
) * telluronium, (protonated hydrogen telluride)


Group 17 (halogen) onium cations, halonium ions, H2X+ (protonated

hydrogen halide In chemistry, hydrogen halides (hydrohalic acids when in the aqueous phase) are diatomic, inorganic compounds that function as Arrhenius acids. The formula is HX where X is one of the halogens: fluorine, chlorine, bromine, iodine, or astatine. ...
s)

* fluoronium, (protonated
hydrogen fluoride Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock ...
) * chloronium, (protonated
hydrogen chloride The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chlorid ...
) * bromonium, (protonated
hydrogen bromide Hydrogen bromide is the inorganic compound with the formula . It is a hydrogen halide consisting of hydrogen and bromine. A colorless gas, it dissolves in water, forming hydrobromic acid, which is saturated at 68.85% HBr by weight at room tem ...
) * iodonium, (protonated
hydrogen iodide Hydrogen iodide () is a diatomic molecule and hydrogen halide. Aqueous solutions of HI are known as hydroiodic acid or hydriodic acid, a strong acid. Hydrogen iodide and hydroiodic acid are, however, different in that the former is a gas under ...
)


Pseudohalogen Pseudohalogens are polyatomic analogues of halogens, whose chemistry, resembling that of the true halogens, allows them to substitute for halogens in several classes of chemical compounds. Pseudohalogens occur in pseudohalogen molecules, inorganic ...
onium cations

* aminodiazonium, (protonated hydrogen azide) *methylidyneammonium/hydrocyanonium, , isomers HC≡NH+ and N≡CH (protonated
hydrogen cyanide Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure . It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at . HCN is produced on a ...
)


Group 18 (noble gas) onium cations

*
hydrohelium The helium hydride ion or hydridohelium(1+) ion or helonium is a cation ( positively charged ion) with chemical formula HeH+. It consists of a helium atom bonded to a hydrogen atom, with one electron removed. It can also be viewed as protonated ...
or helonium, better known as helium hydride ion, HeH+ (protonated
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
) *
neonium Neon compounds are chemical compounds containing the element neon (Ne) with other molecules or elements from the periodic table. Compounds of the noble gas neon were believed not to exist, but there are now known to be molecular ions containing ne ...
, NeH+ (protonated
neon Neon is a chemical element with the symbol Ne and atomic number 10. It is a noble gas. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with about two-thirds the density of air. It was discovered (along with krypt ...
) * argonium, ArH+ (protonated
argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...
) *
kryptonium Kryptonite is a fictional material that appears primarily in Superman stories published by DC Comics. In its best-known form, it is a green, crystalline material originating from Superman's home world of Krypton that emits a unique, poisonou ...
, KrH+ (protonated
krypton Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is of ...
) *
xenonium The xenonium ion, XeH+, is an onium compound, consisting of protonated xenon. Although the existence of the xenonium cation itself has not been proven, salts of the fluoroxenonium ion, XeF+, are known to exist, for instance fluoroxenonium pentafluo ...
, XeH+ (protonated
xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
) *trifluoroxenonium, ( is neutral.)


Hydrogen onium cation

*hydrogenonium, better known as trihydrogen cation, H (protonated molecular or diatomic
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
), found in ionized hydrogen and interstellar space


Onium cations with monovalent substitutions

*primary ammonium cations, RH3N+ or RNH (protonated primary
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
s) ** hydroxylammonium, NH3OH+ (protonated
hydroxylamine Hydroxylamine is an inorganic compound with the formula . The material is a white crystalline, hygroscopic compound.Greenwood and Earnshaw. ''Chemistry of the Elements.'' 2nd Edition. Reed Educational and Professional Publishing Ltd. pp. 431–43 ...
) ** methylammonium, CH3NH (protonated
methylamine Methylamine is an organic compound with a formula of . This colorless gas is a derivative of ammonia, but with one hydrogen atom being replaced by a methyl group. It is the simplest primary amine. Methylamine is sold as a solution in methanol, ...
) ** ethylammonium, C2H5NH (protonated
ethylamine Ethylamine, also known as ethanamine, is an organic compound with the formula CH3CH2NH2. This colourless gas has a strong ammonia-like odor. It condenses just below room temperature to a liquid miscible with virtually all solvents. It is a nucl ...
) ** hydrazinium, or diazanium, NH2NH (protonated
hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
, a.k.a. diazane) **anilinium (a.k.a. phenylammonium), (protonated
aniline Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine. It is an industrially significant commodity chemical, as well as a versatile starti ...
, a.k.a. phenylamine, aminobenzene) *secondary ammonium cations, R2NH (protonated secondary
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
s) ** dimethylammonium (sometimes dimethylaminium), (CH3)2NH (protonated
dimethylamine Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to arou ...
) ** diethylammonium (sometimes diethylaminium), (C2H5)2NH (protonated diethylamine) ** ethylmethylammonium, C2H5CH3NH (protonated ethylmethylamine) ** diethanolammonium (sometimes diethanolaminium), (C2H4OH)2NH (protonated
diethanolamine Diethanolamine, often abbreviated as DEA or DEOA, is an organic compound with the formula HN(CH2CH2OH)2. Pure diethanolamine is a white solid at room temperature, but its tendencies to absorb water and to supercool meaning that it is often encou ...
) *tertiary ammonium cations, R3NH+ (protonated tertiary
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
s) **
trimethylammonium Trimethylamine (TMA) is an organic compound with the formula N(CH3)3. It is a colorless, hygroscopic, and flammable tertiary amine. It is a gas at room temperature but is usually sold as a 40% solution in water. (It is also sold in pressurized ...
(CH3)3NH+ (protonated
trimethylamine Trimethylamine (TMA) is an organic compound with the formula N(CH3)3. It is a colorless, hygroscopic, and flammable tertiary amine. It is a gas at room temperature but is usually sold as a 40% solution in water. (It is also sold in pressurized ...
) ** triethylammonium (C2H5)3NH+ (protonated
triethylamine Triethylamine is the chemical compound with the formula N(CH2CH3)3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine or tetraethylammonium, for which TEA ...
) *
quaternary ammonium cation In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cation ...
s, R4N+ or NR ** tetrafluoroammonium, NF ** tetramethylammonium, (CH3)4N+ ** tetraethylammonium, (C2H5)4N+ ** tetrapropylammonium, (C3H7)4N+ ** tetrabutylammonium, (C4H9)4N+ or abbreviated Bu4N+ **
trimethyl ammonium compounds Trimethyl ammonium compounds are a type of quaternary ammonium compound with three methyl groups at the nitrogen, with a more complicated carbon chain derivative at the fourth position. Examples include: * Betaine * Bethanechol * Carnitine and ...
, (CH3)3RN+ ** didecyldimethylammonium, (C10H21)2(CH3)2N+ ** pentamethylhydrazinium, N(CH3)2N(CH3) *quaternary phosphonium cations, R4P+ or PR ** tetraphenylphosphonium, *primary oxonium cations, (protonated R-O-H oxygen compounds) **alkyloxonium cations (protonated
alcohols In chemistry, an alcohol is a type of organic compound that carries at least one hydroxyl () functional group bound to a saturated carbon atom. The term ''alcohol'' originally referred to the primary alcohol ethanol (ethyl alcohol), which is ...
) ***methyloxonium, (protonated
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is ...
) ***ethyloxonium, (protonated
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
) *secondary oxonium cations, (protonated R-O-R oxygen compounds) **dialkyloxonium cations (protonated
ether In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again ...
s) ***dimethyloxonium, (protonated
dimethyl ether Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3, (sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor ...
) *tertiary oxonium cations, **
trifluorooxonium The trifluorooxonium cation is a hypothetical positively charged polyatomic ion with chemical formula . It is structurally equivalent to the hydronium ion where the hydrogen atoms surrounding the central oxygen atom have been replaced by fluorine, ...
, (hypothetical) ** trimethyloxonium, ** triethyloxonium, **
oxatriquinacene Oxatriquinacene is an organic cation with formula . It is an oxonium ion, with a trivalent oxygen atom with +1 charge connected to carbons 1,4, and 7 of a cyclononatriene ring, forming three fused pentagonal cycles. The compound may possess we ...
, (cyclic) **
oxatriquinane Oxatriquinane (oxoniaperhydrotriquinacene) is an alkyl oxonium ion with formula (CH2CH2CH)3O+. It has a cyclononane backbone, with a trivalent oxygen connected to carbon 1, 4, and 7, forming three fused pentagonal rings. In contrast to most tria ...
, (cyclic) *secondary sulfonium cations, R2SH+ (protonated
sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
s) ** dimethylsulfonium, (CH3)2SH+ (protonated
dimethyl sulfide Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula (CH3)2S. Dimethyl sulfide is a flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from co ...
) *tertiary sulfonium cations, R3S+ ** trimethylsulfonium, (CH3)3S+ *secondary fluoronium cations, R2F+ ** dichlorofluoronium, Cl2F+


Onium cations with polyvalent substitutions

*secondary ammonium cations having one double-bonded substitution, **diazenium, (protonated diazene) ** guanidinium, (protonated guanidine) (has a
resonance Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscil ...
structure) *tertiary ammonium cations having one triple-bonded substitution, R≡NH+ ** nitrilium, RC≡NH+ (protonated
nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix '' cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including me ...
) ** diazonium, N≡NH+ (protonated
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
) *tertiary ammonium cations having two partially double-bonded substitutions, RNH+R ** pyridinium, C5H5NH+ (protonated
pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid w ...
) *quaternary ammonium cations having one double-bonded substitution and two single-bonded substitutions, ** iminium, (substituted protonated imine) **diazenium, (substituted protonated diazene) **thiazolium, (substituted protonated
thiazole Thiazole, or 1,3-thiazole, is a heterocyclic compound that contains both sulfur and nitrogen. The term 'thiazole' also refers to a large family of derivatives. Thiazole itself is a pale yellow liquid with a pyridine-like odor and the molecular fo ...
) *quaternary ammonium cations having two double-bonded substitutions, R=N=R+ **
nitronium The nitronium ion, , is a cation. It is an onium ion because its nitrogen atom has +1 charge, similar to ammonium ion . It is created by the removal of an electron from the paramagnetic nitrogen dioxide molecule , or the protonation of nitri ...
, ** bis(triphenylphosphine)iminium, ((C6H5)3P)2N+ *quaternary ammonium cations having one triple-bonded substitution and one single-bonded substitution, R≡NR+ ** diazonium, N≡NR+ (substituted protonated nitrogen) **nitrilium, RC≡NR+ (substituted protonated nitrile) *tertiary oxonium cations having one triple-bonded substitution, R≡O+ **
acylium ion In chemistry, an acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an alkyl group (). In organic chemistry, the acyl group (IUPAC ...
s, R−C≡O+ ↔ R−C+=O **
nitrosonium The nitrosonium ion is , in which the nitrogen atom is bonded to an oxygen atom with a bond order of 3, and the overall diatomic species bears a positive charge. It can be viewed as nitric oxide with one electron removed. This ion is usually ob ...
, N≡O+ *tertiary oxonium cations having two partially double-bonded substitutions, RO+R ** pyrylium, C5H5O+ *tertiary sulfonium cations having one triple-bonded substitution, R≡S+ ** thionitrosyl, N≡S+


Double onium dications

* hydrazinediium or hydrazinium(2+) dication, +H3NNH (doubly protonated hydrazine) * diazenediium cation, +H2N=NH (doubly protonated diazene) * diazynediium cation, +HN≡NH+ (doubly protonated iitrogen)


Enium cations

The extra bond is added to a less-common parent hydride, a
carbene analog Carbene analogs in chemistry are carbenes with the carbon atom replaced by another chemical element. Just as regular carbenes they appear in chemical reactions as reactive intermediates and with special precautions they can be stabilized and isolate ...
, typically named ''-ene'' or ''-ylene'', which is neutral with 2 fewer bonds than the more-common hydride, typically named ''-ane'' or ''-ine''. * borenium cations, (protonated
borylene A borylene is the boron analogue of a carbene. The general structure is R-B: with R an organic residue and B a boron atom with two unshared electrons. Borylenes are of academic interest in organoboron chemistry. A singlet ground state is predomin ...
s a.k.a. boranylidenes) *
carbenium A carbenium ion is a positive ion with the structure RR′R″C+, that is, a chemical species with a trivalent carbon that bears a +1 formal charge. In older literature the name carbonium ion was used for this class, but now it refers exclusivel ...
cations, (protonated
carbene In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms. The term "carbene" m ...
s) have a trivalent carbon atom with a +1 charge. **alkenium cations, (''n'' ≥ 2) (protonated
alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic ...
s) *** methenium cation, (protonated methylene) ***
ethenium In chemistry, ethenium, protonated ethylene or ethyl cation is a positive ion with the formula . It can be viewed as a molecule of ethylene () with one added proton (), or a molecule of ethane () minus one hydride ion (). It is a carbocation; mo ...
, (protonated
ethene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene i ...
) **
benzenium An arenium ion in organic chemistry is a cyclohexadienyl cation that appears as a reactive intermediate in electrophilic aromatic substitution. For historic reasons this complex is also called a Wheland intermediate, after American chemist George ...
, (protonated
benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
) **
tropylium In organic chemistry, the tropylium ion or cycloheptatrienyl cation is an aromatic species with a formula of 7H7sup>+. Its name derives from the molecule tropine from which cycloheptatriene (tropylidene) was first synthesized in 1881. Salts of ...
, * silylium cations, (protonated
silylene Silylene is a chemical compound with the formula SiH2. It is the silicon analog of methylene, the simplest carbene. Silylene is a stable molecule as a gas but rapidly reacts in a bimolecular manner when condensed. Unlike carbenes, which can exis ...
s) * nitrenium cations, (protonated nitrenes) * phosphinidenium cations, (protonated phosphinidene) * mercurinium cations, (protonated organomercury compounds; formed as intermediates in oxymercuration reactions)


Substituted eniums

*diphenylcarbenium, (di-substituted methenium) *
triphenylcarbenium In chemistry, triphenylcarbenium, triphenylmethyl cation, tritylium , or trityl cation is an ion with formula or , consisting of a carbon atom with a positive charge connected to three phenyl groups. It is a charged version of the triphenylmethy ...
, (tri-substituted methenium)


Ynium cations

* carbynium ions (protonated carbynes) have a divalent carbon atom with a +1 charge. **alkynium cations, (''n'' ≥ 2) (protonated
alkyne \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...
s) *** methynium cation, (protonated methylidyne radical) *** ethynium, (protonated
ethyne Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
)


See also

*
Carbonium ion In chemistry, a carbonium ion is any cation that has a pentavalent carbon atom. The name carbonium may also be used for the simplest member of the class, properly called methanium (), where the five valences are filled with hydrogen atoms. The ...
*
Lyonium ion In chemistry, a lyonium ion is the cation derived by the protonation of a solvent molecule. For example, a hydronium ion is formed by the protonation of water, and is the cation formed by the protonation of methanol. Its counterpart is a lya ...
, a protonated solvent molecule *
Lyate ion In chemistry, a lyate ion is the anion derived by the deprotonation of a solvent molecule. For example, a hydroxide ion is formed by the deprotonation of water, and methoxide () is the anion formed by the deprotonation of methanol. Its counterp ...
, a deprotonated solvent molecule


References


External links


Ions and Radicals
Queen Mary University of London * {{Authority control Cations Chemical nomenclature