Onium compounds
Encyclopedia
Onium compounds are cations derived by the protonation
of mononuclear parent hydride
s of elements of the nitrogen group
(Group 15), chalcogen
s (Group 16), or halogen
s (Group 17), and similar cations derived by the substitution of hydrogen atoms in the former by other groups, such as organic radicals, or halogens, for example tetramethylammonium, and further derivatives having polyvalent additions, such as iminium
and nitrilium
. (IUPAC definition http://goldbook.iupac.org/O04291.html; other definitions vary.)
They are also known as onium ions. Compounds of these ions are known as onium salts. Onium ions have a charge of +1; double onium ions have a charge of +2, and so on.
Protonation
In chemistry, protonation is the addition of a proton to an atom, molecule, or ion. Some classic examples include*the protonation of water by sulfuric acid:*the protonation of isobutene in the formation of a carbocation:2C=CH2 + HBF4 → 3C+ + BF4−*the protonation of ammonia in the...
of mononuclear parent hydride
Hydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...
s of elements of the nitrogen group
Nitrogen group
The nitrogen group is a periodic table group consisting of nitrogen , phosphorus , arsenic , antimony , bismuth and ununpentium ....
(Group 15), chalcogen
Chalcogen
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family...
s (Group 16), or halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
s (Group 17), and similar cations derived by the substitution of hydrogen atoms in the former by other groups, such as organic radicals, or halogens, for example tetramethylammonium, and further derivatives having polyvalent additions, such as iminium
Iminium
An iminium salt or cation in organic chemistry has the general structure [R1R2C=NR3R4]+ and is as such a protonated or substituted imine. It is an intermediate in many organic reactions such as the Beckmann rearrangement, Vilsmeier-Haack reaction, Stephen reaction or the Duff reaction...
and nitrilium
Nitrilium
A nitrilium ion is a nitrile that has been protonated, [RCNH]+, or alkylated, [RCNR′]+.-Synthesis:Nitriles are only weakly basic and are poor nucleophiles, but they will attack very reactive electrophiles such as carbocations....
. (IUPAC definition http://goldbook.iupac.org/O04291.html; other definitions vary.)
They are also known as onium ions. Compounds of these ions are known as onium salts. Onium ions have a charge of +1; double onium ions have a charge of +2, and so on.
Simple onium cations
- Group 15 (nitrogen group) onium cations:
- ammoniumAmmoniumThe ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
, a.k.a. azanium, (protonated ammoniaAmmoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
, a.k.a. azane) - phosphoniumPhosphoniumThe phosphonium cation describes positively charged polyatomic cations with the chemical formula . Salts of the parent PH4+ are rarely encountered, but this ion is an intermediate in the preparation of the industrially useful tetrakisphosphonium chloride:Organic phosphonium salts are common...
, (protonated phosphinePhosphinePhosphine is the compound with the chemical formula PH3. It is a colorless, flammable, toxic gas. Pure phosphine is odourless, but technical grade samples have a highly unpleasant odor like garlic or rotting fish, due to the presence of substituted phosphine and diphosphine...
) - arsonium, (protonated arsineArsineArsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...
) - stibonium, (protonated stibineStibineStibine is the chemical compound with the formula SbH3. This colourless gas is the principal covalent hydride of antimony and a heavy analogue of ammonia. The molecule is pyramidal with H–Sb–H angles of 91.7° and Sb–H distances of 1.707 Å...
) - bismuthonium, (protonated bismuthineBismuthineBismuthine is the chemical compound with the formula BiH3. As the heaviest analogue of ammonia, BiH3 is unstable, decomposing to bismuth metal well below 0 °C...
)
- ammonium
- Group 16 (chalcogen) onium cations:
- oxoniumOxonium ionThe oxonium ion in chemistry is any oxygen cation with three bonds. The simplest oxonium ion is the hydronium ion H3O+. Another oxonium ion frequently encountered in organic chemistry is obtained by protonation or alkylation of a carbonyl group e.g...
, better known as hydroniumHydroniumIn chemistry, a hydronium ion is the cation , a type of oxonium ion produced by protonation of water. This cation is often used to represent the nature of the proton in aqueous solution, where the proton is highly solvated...
, (protonated water) (Hydronium implies a solvatedSolvationSolvation, also sometimes called dissolution, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute...
or hydrated proton.) (May be called hydroxonium for disambiguation.) - sulfoniumSulfoniumA sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively charged ion featuring three organic substituents attached to sulfur. They have the formula [SR3]+...
, (protonated hydrogen sulfideHydrogen sulfideHydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
) - selenonium, (protonated hydrogen selenideHydrogen selenideHydrogen selenide is the inorganic compound with the formula H2Se. It is the simplest and virtually the only hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic selenium compound with an exposure limit: 0.05 ppm over an 8 hour period...
) - telluronium, (protonated hydrogen tellurideHydrogen tellurideHydrogen telluride is the inorganic compound with the formula H2Te. The simplest hydride of tellurium, it is rarely encountered because of it decomposes rapidly to the constituent elements. Most compounds with Te-H bonds are unstable with respect to loss of H2. H2Te is chemically and structurally...
)
- oxonium
- Group 17 (halogen) onium cations, halonium ionHalonium ionA halonium ion in organic chemistry is any onium compound containing a halogen atom carrying a positive charge. This cation has the general structure R-X+-R where X is any halogen and R any organic residue and this structure can be cyclic or an open chain molecular structure...
s, (protonated hydrogen halideHydrogen halideHydrogen halides are acids resulting from the chemical reaction of hydrogen with one of the halogen elements , which are found in Group 17 of the periodic table. Astatine is not included in the list because it is very rare, unstable and not found as the acid in substantial quantities...
s)- fluoroniumFluoroniumThe fluoronium cation, H2F+, is a polyatomic ion formed by protonation or self-ionic dissociation of hydrogen fluoride:orUnlike for halonium ions based on chlorine, bromine or iodine , hydrocarbyl derivatives of fluoronium, i.e. R2F+, remain unknown....
, (protonated hydrogen fluorideHydrogen fluorideHydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...
) - chloronium, (protonated hydrogen chlorideHydrogen chlorideThe compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
) - bromonium, (protonated hydrogen bromideHydrogen bromideHydrogen bromide is the diatomic molecule HBr. HBr is a gas at standard conditions. Hydrobromic acid forms upon dissolving HBr in water. Conversely, HBr can be liberated from hydrobromic acid solutions with the addition of a dehydration agent, but not by distillation. Hydrogen bromide and...
) - iodonium, (protonated hydrogen iodideHydrogen iodideHydrogen iodide is a diatomic molecule. Aqueous solutions of HI are known as iohydroic acid or hydroiodic acid, a strong acid. Gas and aqueous solution are interconvertible...
)
- fluoronium
- Group 14 (carbon group) onium cations (these ions use similar naming schemes. they do not strictly meet the IUPAC definition above):
- methanium, (protonated methaneMethaneMethane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
) (Sometimes methonium, but it has multiple definitions.) (Should not be called carboniumCarbonium ionA carbonium ion is a carbocation of the penta- or tetracoordinated nonclassical type such as an ion of the type R5C+.- Methanium:The parent compound methanium or CH5+ is protonated methane and a superacid. This ion exists as a reactive intermediate in the interstellar medium and can be produced in...
http://goldbook.iupac.org/C00839.html.) (Abundant in outer space.) - further alkanium cations, CnH(2n+3)+
- ethanium, (protonated ethaneEthaneEthane is a chemical compound with chemical formula C2H6. It is the only two-carbon alkane that is an aliphatic hydrocarbon. At standard temperature and pressure, ethane is a colorless, odorless gas....
) - propanium, (propanePropanePropane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...
protonated on an unspecified carbon)- propylium, a.k.a. propan-1-ylium (propane protonated on an end carbon)
- propan-2-ylium (propane protonated on the middle carbon)
- ethanium, (protonated ethane
- silanium (sometimes silonium), (protonated silaneSilaneSilane is a toxic, extremely flammable chemical compound with chemical formula SiH4. In 1857, the German chemists and Friedrich Woehler discovered silane among the products formed by the action of hydrochloric acid on aluminum silicide, which they had previously prepared...
) (Should not be called siliconium.http://www.chem.qmul.ac.uk/iupac/ions/RC821.html) - germonium, (protonated germaneGermaneGermane is the chemical compound with the formula GeH4, 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 tetrahedral. It burns in air to produce GeO2 and...
) - stannonium, (protonated ; not protonated stannaneStannaneStannane is the hydride of tin. Stannane can be prepared by the reaction of SnCl4 and LiAlH4. Stannane decomposes slowly at room temperature to give metallic tin and hydrogen and ignites on contact with air....
)
- methanium, (protonated methane
- Group 13Group 13"The Group Thirteen" network was a Jewish collaborationist organisation in the Warsaw Ghetto during the Second World War. The Thirteen took its informal name from the address of its main office in Leszno Street 13. The group was founded in December 1940 and led by Abraham Gancwajch, the former...
(boron group) onium cations (these ions use a similar naming scheme. they do not strictly meet the IUPAC definition above):- boronium cations, , , , (protonated boraneBoraneIn chemistry, a borane is a chemical compound of boron and hydrogen. The boranes comprise a large group of compounds with the generic formulae of BxHy. These compounds do not occur in nature. Many of the boranes readily oxidise on contact with air, some violently. The parent member BH3 is called...
s)
- boronium cations, , , , (protonated borane
- Hydrogen onium cation (this ion uses a similar naming scheme. it does not strictly meet the IUPAC definition above):
- hydrogenonium, better known as trihydrogen cation, (protonated [molecular] or [diatomic] hydrogenHydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
). (Abundant in outer space.)
- hydrogenonium, better known as trihydrogen cation, (protonated [molecular] or [diatomic] hydrogen
Onium cations with monovalent substitutions
- primary ammonium cations, or (protonated primary amineAmineAmines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
s)- hydroxylammoniumHydroxylammonium nitrateHydroxylammonium nitrate or hydroxylamine nitrate is an energetic chemical with the chemical formula NH3OHNO3. It is the salt of hydroxylamine and nitric acid. It is related to ammonium nitrate, but has a higher oxygen content...
, (protonated hydroxylamineHydroxylamineHydroxylamine is an inorganic compound with the formula NH2OH. The pure material is a white, unstable crystalline, hygroscopic compound. However, hydroxylamine is almost always provided and used as an aqueous solution. It is used to prepare oximes, an important functional group. It is also an...
) - methylammonium, (protonated methylamineMethylamineMethylamine is the organic compound with a formula of CH3NH2. This colourless gas is a derivative of ammonia, but with one H atom replaced by a methyl group. It is the simplest primary amine. It is sold as a solution in methanol, ethanol, THF, and water, or as the anhydrous gas in pressurized...
) - ethylammoniumEthylammonium nitrateEthylammonium nitrate or ethylamine nitrate is a salt with formula or ·. It is an odorless and colorless to slightly yellowish liquid with a melting point of 12 °C...
, (protonated ethylamineEthylamineEthylamine is an organic compound with the formula CH3CH2NH2. This colourless gas has a strong ammonia-like odor. It is miscible with virtually all solvents and is considered to be a weak base, as is typical for amines. Ethylamine is widely used in chemical industry and organic...
) - hydrazinium, a.k.a. diazanium, (protonated hydrazineHydrazineHydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
, a.k.a. diazane)
- hydroxylammonium
- secondary ammonium cations, (protonated secondary amineAmineAmines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
s)- dimethylammonium (sometimes dimethylaminium), (protonated dimethylamineDimethylamineDimethylamine is an organic compound with the formula 2NH. This secondary amine is a colorless, flammable liquified gas with an ammonia-like odor. Dimethylamine is generally encountered as a solution in water at concentrations up to around 40%...
) - diethylammonium (sometimes diethylaminium), (protonated diethylamineDiethylamineDiethylamine is a secondary amine with the molecular structure CH3CH2NHCH2CH3. It is a flammable, strongly alkaline liquid. It is miscible with water and ethanol. It is a colorless liquid which often appears brown due to impurities...
) - ethylmethylammonium, (protonated ethylmethylamine)
- diethanolammonium (sometimes diethanolaminium), (protonated diethanolamine)
- dimethylammonium (sometimes dimethylaminium), (protonated dimethylamine
- tertiary ammonium cations, (protonated tertiary amineAmineAmines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
s)- trimethylammonium (protonated trimethylamineTrimethylamineTrimethylamine is an organic compound with the formula N3. This colorless, hygroscopic, and flammable tertiary amine has a strong "fishy" odor in low concentrations and an ammonia-like odor at higher concentrations...
) - triethylammonium (protonated triethylamineTriethylamineTriethylamine is the chemical compound with the formula N3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine, for which TEA is also a common abbreviation....
)
- trimethylammonium (protonated trimethylamine
- quaternary ammonium cationQuaternary ammonium cationQuaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure NR4+, R being an alkyl group or an aryl group. Unlike the ammonium ion and the primary, secondary, or tertiary ammonium cations, the quaternary ammonium cations are permanently charged,...
s, or- tetramethylammoniumTetramethylammonium hydroxideTetramethylammonium hydroxide is a quaternary ammonium salt with the molecular formula 4NOH. It is used as an anisotropic etchant of silicon. It is also used as a basic solvent in the development of acidic photoresist in the photolithography process. Since it is a phase transfer catalyst, it is...
, - tetraethylammoniumTetraethylammoniumTetraethylammonium is a quaternary ammonium cation consisting of four ethyl groups attached to a central nitrogen atom. Like other members of its class, it can be used to alter a compound's solubility by displacing hard acids with this comparatively softer acid...
, - tetrapropylammonium,
- tetrabutylammoniumTetrabutylammonium hydroxideTetrabutylammonium hydroxide is the chemical compound with the formula 4NOH, abbreviated Bu4NOH with the acronym TBAOH or TBAH. This species is not readily obtainable as a pure compound, but it employed as a solution in water or alcohols. It is commonly used as a base in organic chemistry...
, or abbreviated - trimethyl ammonium compoundsTrimethyl ammonium compoundsTrimethyl 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...
, - didecyldimethylammoniumDidecyldimethylammonium chlorideDidecyldimethylammonium chloride is an antiseptic/disinfectant, which is used in many biocidal applications. They cause disruption of intermolecular interactions and dissociation of lipid bilayers. They are Broad spectrum Bactericidal and Fungicidal.They can be used as Disinfectant Cleaner for...
, - pentamethylhydrazinium,
- tetramethylammonium
- quaternary phosphonium cations, or
- tetraphenylphosphonium,
- secondary sulfonium cations, (protonated sulfideSulfideA sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
s)- dimethylsulfonium, (protonated dimethyl sulfideDimethyl sulfideDimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...
)
- dimethylsulfonium, (protonated dimethyl sulfide
- tertiary sulfonium cations,
- trimethylsulfoniumTrimethylsulfoniumTrimethylsulfonium is a cationic chemical compound with the molecular formula 3S+.Several salts of trimethyl sulfonium are known:-References:...
,
- trimethylsulfonium
- secondary fluoronium cations,
- dichlorofluoronium,
Onium cations with polyvalent substitutions
- secondary ammonium cations having one double-bonded substitution, R=NH2+
- diazenium, HN=NH2+ (protonated diazeneDiazeneDiazene, also called diimine or diimide, is a compound having the formula 2. It exists as two geometric isomers, E and Z. Diazene is also the parent member of the entire class of azo compounds with the formula 2, where R is an organyl group...
)
- diazenium, HN=NH2+ (protonated diazene
- quaternary ammonium cations having one double-bonded substitution and two single-bonded substitutions, R=NR2+
- iminiumIminiumAn iminium salt or cation in organic chemistry has the general structure [R1R2C=NR3R4]+ and is as such a protonated or substituted imine. It is an intermediate in many organic reactions such as the Beckmann rearrangement, Vilsmeier-Haack reaction, Stephen reaction or the Duff reaction...
, R2C=NR2+ (substituted protonated imineImineAn imine is a functional group or chemical compound containing a carbon–nitrogen double bond, with the nitrogen attached to a hydrogen atom or an organic group. If this group is not a hydrogen atom, then the compound is known as a Schiff base...
) - diazenium, RN=NR2+ (substituted protonated diazeneDiazeneDiazene, also called diimine or diimide, is a compound having the formula 2. It exists as two geometric isomers, E and Z. Diazene is also the parent member of the entire class of azo compounds with the formula 2, where R is an organyl group...
)
- iminium
- quaternary ammonium cations having two double-bonded substitutions, R=N=R+
- nitroniumNitronium ionThe nitronium ion, or sometimes the nitryl ion , , is a generally reactive cation created by the removal of an electron from the paramagnetic nitrogen dioxide molecule, or the protonation of nitric acid....
, - bis(triphenylphosphine)iminium,
- nitronium
- tertiary ammonium cations having one triple-bonded substitution, R≡NH+
- nitriliumNitriliumA nitrilium ion is a nitrile that has been protonated, [RCNH]+, or alkylated, [RCNR′]+.-Synthesis:Nitriles are only weakly basic and are poor nucleophiles, but they will attack very reactive electrophiles such as carbocations....
, RC≡NH+ (protonated nitrileNitrileA nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
)
- nitrilium
- quaternary ammonium cations having one triple-bonded substitution and one single-bonded substitution, R≡NR+
- diazoniumDiazonium compoundDiazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group R-N2+ X- where R can be any organic residue such alkyl or aryl and X is an inorganic or organic anion such as a halogen...
, N≡NR+ (substituted protonated nitrogenNitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
) - nitrilium, RC≡NR+ (substituted protonated nitrileNitrileA nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
)
- diazonium
- ternary oxonium cations having one triple-bonded substitution, R≡O+
- nitrosoniumNitrosoniumThe nitrosonium ion is NO+, 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. This ion is usually obtained as the following salts: NOClO4, NOSO4H , and NOBF4. The ClO and BF salts are slightly soluble in CH3CN...
, N≡O+
- nitrosonium
- tertiary sulfonium cations having one triple-bonded substitution, R≡S+
- thionitrosyl, N≡S+
Double-onium dications
- hydrazinium dicationDicationA dication is any cation, of general formula 2+, formed by the removal of two electrons from a neutral species.Diatomic dications corresponding to stable neutral species often decay quickly into two singly charged particles , due to the loss of electrons in bonding molecular orbitals...
, +H3NNH3+ (doubly protonated hydrazineHydrazineHydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
) - diazenium dication, +H2N=NH2+ (doubly protonated diazeneDiazeneDiazene, also called diimine or diimide, is a compound having the formula 2. It exists as two geometric isomers, E and Z. Diazene is also the parent member of the entire class of azo compounds with the formula 2, where R is an organyl group...
) - diazoniumDiazonium compoundDiazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group R-N2+ X- where R can be any organic residue such alkyl or aryl and X is an inorganic or organic anion such as a halogen...
dication, +HN≡NH+ (doubly protonated nitrogenNitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
)