The nitronium ion, , is a
cation. It is an
onium ion 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 nitrogen dioxide 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 of
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 of other substances. The
ion is generated ''
in situ'' 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
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 ...
according to the
equilibrium:
:
Structure
The nitronium ion is
isoelectronic 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, 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 can be isolated. These include
nitronium perchlorate ,
nitronium tetrafluoroborate , nitronium
hexafluorophosphate , nitronium
hexafluoroarsenate , and nitronium
hexafluoroantimonate . These are all very
hygroscopic compounds.
The solid form of
dinitrogen pentoxide, , 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 ...
or
gaseous state is
molecular and does not contain nitronium ions.
[
]
Related species
The compounds nitryl fluoride, , and nitryl chloride, , 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 radical, ; in fact, this is fairly stable and known as the compound nitrogen dioxide.
The related negatively charged species is , the nitrite ion.
See also
* Nitrosonium
References
{{Nitrogen compounds
Oxycations
Nitronium compounds
Functional groups
Nitrogen(V) compounds