The nitronium 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 convent ...

. It is an

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 nam ...

because its nitrogen atom has +1 charge, similar to

ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...

ion . It is created by the removal of an electron from the

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...

nitrogen dioxide Nitrogen dioxide is a chemical compound with the formula . One of several nitrogen oxides, nitrogen dioxide is a reddish-brown gas. It is a paramagnetic, bent molecule with C2v point group symmetry. Industrially, is an intermediate in the s ...

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

, or the

protonation In chemistry, protonation (or hydronation) is the adding of a proton (or hydron, or hydrogen cation), usually denoted by H+, to an atom, molecule, or ion, forming a conjugate acid. (The complementary process, when a proton is removed from a Brø ...

nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...

(with removal of ). It is stable enough to exist in normal conditions, but it is generally reactive and used extensively as an

electrophile In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively Electric charge, charged, have an ...

in the

nitration In organic chemistry, nitration is a general class of chemical processes for the introduction of a nitro group () into an organic compound. The term also is applied incorrectly to the different process of forming nitrate esters () between Alcohol ...

of other substances. The

ion 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 convent ...

is generated ''

in situ is a Latin phrase meaning 'in place' or 'on site', derived from ' ('in') and ' ( ablative of ''situs'', ). The term typically refers to the examination or occurrence of a process within its original context, without relocation. The term is use ...

'' for this purpose by mixing concentrated

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

and concentrated

according to the

equilibrium Equilibrium may refer to: Film and television * ''Equilibrium'' (film), a 2002 science fiction film * '' The Story of Three Loves'', also known as ''Equilibrium'', a 1953 romantic anthology film * "Equilibrium" (''seaQuest 2032'') * ''Equilibr ...

: :

Structure

The nitronium ion is

isoelectronic Isoelectronicity is a phenomenon observed when two or more molecules have the same structure (positions and connectivities among atoms) and the same electronic configurations, but differ by what specific elements are at certain locations in th ...

with

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

and has the same linear structure and bond angle of 180°. For this reason it has a similar vibrational spectrum to carbon dioxide. Historically, the nitronium ion was detected by

Raman spectroscopy Raman spectroscopy () (named after physicist C. V. Raman) is a Spectroscopy, spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Ra ...

, because its symmetric stretch is Raman-active but infrared-inactive. The Raman-active symmetrical stretch was first used to identify the ion in nitrating mixtures.

Salts

A few stable nitronium salts with anions of weak

nucleophilicity In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

can be isolated. These include

nitronium perchlorate Nitronium perchlorate, NO2ClO4, also known as nitryl perchlorate and nitroxyl perchlorate, is an inorganic chemical, the Salt (chemistry), salt of the perchlorate anion and the nitronium ion, nitronium cation. It forms colorless monoclinic crysta ...

nitronium tetrafluoroborate Nitronium tetrafluoroborate is an inorganic compound with formula NO2BF4. It is a salt of nitronium cation and tetrafluoroborate anion. It is a colorless crystalline solid, which reacts with water to form the corrosive acids HF and HNO3. As su ...

, nitronium

hexafluorophosphate Hexafluorophosphate is an fluoroanion, anion with chemical formula of . It is an Octahedral molecular geometry, octahedral species that imparts no color to its salts. is isoelectronic with sulfur hexafluoride, , and the Hexafluorosilicic acid, h ...

, nitronium

hexafluoroarsenate The hexafluoroarsenate (sometimes shortened to fluoroarsenate) anion is a chemical species with formula . Hexafluoroarsenate is relatively inert, being the conjugate base of the notional superacid hexafluoroarsenic acid (). Synthesis The first ...

, and nitronium

hexafluoroantimonate Antimony pentafluoride is the inorganic compound with the formula Sb F5. This colorless, viscous liquid is a strong Lewis acid and a component of the superacid fluoroantimonic acid, formed upon mixing liquid HF with liquid SbF5 in 1:1 ratio. It ...

. These are all very

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...

compounds. The solid form of

dinitrogen pentoxide Dinitrogen pentoxide (also known as nitrogen pentoxide or nitric anhydride) is the chemical compound with the formula . It is one of the binary nitrogen oxides, a family of compounds that contain only nitrogen and oxygen. It exists as colourless c ...

, , actually consists of nitronium and

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

ions, so it is an

ionic compound In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions (Cation, cations) and negatively charged ions (Anion, anions), which results in a compound with no net electric charge (electrica ...

, nitronium nitrate , not a molecular solid. However, dinitrogen pentoxide in

liquid Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...

gas Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure gas'' is made up of individual atoms (e.g. a noble gas like neon) or molecules of either a single type of atom ( elements such as ...

eous state is

molecular A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, ...

and does not contain nitronium ions.

Related species

The compounds

nitryl fluoride Nitryl fluoride, NO2F, is a colourless gas and strong oxidizing agent, which is used as a fluorinating agent and has been proposed as an oxidiser in rocket propellants (though never flown). It is a molecular species, not ionic, consistent with it ...

, , and

nitryl chloride Nitryl chloride is a volatile inorganic compound with formula ClNO2. At standard conditions it is a gas. Formation Nitryl chloride can be formed in the reaction of dinitrogen pentoxide with chlorides or hydrogen chloride: :N2O5 + 2HCl → 2ClNO2 ...

, , are not nitronium salts but molecular compounds, as shown by their low boiling points (−72 °C and −6 °C respectively) and short nitrogen–halogen bond lengths (N–F 135 pm, N–Cl 184 pm). F. A. Cotton and G.Wilkinson, Advanced Inorganic Chemistry, 5th edition (1988), Wiley, p.333 Addition of one electron forms the neutral

nitryl Nitryl is the nitrogen dioxide (NO2) moiety when it occurs in a larger compound as a univalent fragment. Examples include nitryl fluoride (NO2F) and nitryl chloride (NO2Cl). Like nitrogen dioxide, the nitryl moiety contains a nitrogen atom with ...

radical Radical (from Latin: ', root) may refer to: Politics and ideology Politics *Classical radicalism, the Radical Movement that began in late 18th century Britain and spread to continental Europe and Latin America in the 19th century *Radical politics ...

, ; in fact, this is fairly stable and known as the compound

. The related negatively charged species is , the

nitrite The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...

ion.

References

{{Nitrogen compounds Oxycations Nitronium compounds Functional groups Nitrogen(V) compounds

Structure

Salts

Related species

See also

References