Editing Nitronium ion

{{Short description|Polyatomic ion}}
{{Distinguish|Nitrosonium|text=[[Nitrosonium]], a separate nitrogen-oxygen cation}}{{Chembox
|ImageFile2 = Nitronium-3D-balls.png
| ImageClass2 = bg-transparent
|ImageFile2_Ref = {{chemboximage|correct|??}}
|ImageSize2 = 120
|ImageName2 = Ball and stick model of nitronium
|ImageFileL1 = Nitronium-2D-dimensions.png
| ImageClassL1 = skin-invert-image
|ImageFileL1_Ref = {{chemboximage|correct|??}}
|ImageNameL1 = Skeletal formula of nitronium with some dimensions added
|ImageFileR1 = Nitronium-3D-vdW.png
| ImageClassR1 = bg-transparent
|ImageFileR1_Ref = {{chemboximage|correct|??}}
|IUPACName=Nitronium ion
|ImageNameR1 = Spacefill model of nitronium
|SystematicName = Dioxidonitrogen(1+)<ref>{{Cite web |url= http://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:29424|title= dioxidonitrogen(1+) (CHEBI:29424)|work= Chemical Entities of Biological Interest (ChEBI)|location= UK|publisher =European Bioinformatics Institute}}</ref>
|Section1={{Chembox Identifiers
|CASNo = 12269-46-4
|PubChem = 3609161
|ChemSpiderID = 2844644
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChEBI = 29424
|SMILES = O=[N+]=O
|StdInChI = 1S/NO2/c2-1-3/q+1
|StdInChIKey = OMBRFUXPXNIUCZ-UHFFFAOYSA-N
}}
|Section2={{Chembox Properties
|Formula = {{chem2|[NO2]+}}
|N=1|O=2
}}
|Section3={{Chembox Thermochemistry
|Entropy = 233.86 J K<sup>−1</sup> mol<sup>−1</sup>
}}
}}

The '''nitronium ion''', {{chem2|auto=1|[NO2]+}}, is a [[cation]]. It is an [[onium ion]] because its nitrogen atom has +1 charge, similar to [[ammonium]] ion {{chem2|[NH4]+}}. It is created by the removal of an electron from the [[paramagnetic]] [[nitrogen dioxide]] [[molecule]] {{chem2|NO2}}, or the [[protonation]] of [[nitric acid]] {{chem2|HNO3}} (with removal of {{chem2|H2O}}).<ref name=G&E>{{Greenwood&Earnshaw2nd}}</ref>

It is stable enough to exist in normal conditions, but it is generally reactive and used extensively as an [[electrophile]] in the [[nitration]] of other substances. The [[ion]] is generated ''[[in situ]]'' for this purpose by mixing concentrated [[sulfuric acid]] and concentrated [[nitric acid]] according to the [[chemical equilibrium|equilibrium]]:

:{{chem2|H2SO4 + HNO3 → HSO4− + [NO2]+ + H2O}}

== Structure ==
The nitronium ion is [[isoelectronicity|isoelectronic]] with [[carbon dioxide]] 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.<ref>{{cite journal |last1=Ingold |first1=C. K. |last2=Millen |first2=D. J. |last3=Poole |first3=H. G. |title=Spectroscopic Identification of the Nitronium Ion |journal=Nature |date=1946 |volume=158 |issue=4014 |pages=480–481|doi=10.1038/158480c0 |bibcode=1946Natur.158..480I |s2cid=4106964 }}</ref>

== Salts ==
A few stable nitronium salts with anions of weak [[nucleophile|nucleophilicity]] can be isolated. These include [[nitronium perchlorate]] {{chem2|[NO2]+[ClO4]-}}, [[nitronium tetrafluoroborate]] {{chem2|[NO2]+[BF4]-}}, nitronium [[hexafluorophosphate]] {{chem2|[NO2]+[PF6]-}}, nitronium [[hexafluoroarsenate]] {{chem2|[NO2]+[AsF6]-}}, and nitronium [[fluoroantimonic acid|hexafluoroantimonate]] {{chem2|[NO2]+[SbF6]-}}. These are all very [[hygroscopic]] compounds.<ref>{{cite book |title= Aromatic nitration |author= Kenneth Schofield |publisher= CUP Archive |year= 1980 |isbn= 0-521-23362-3 |page= 88 }}</ref>

The solid form of [[dinitrogen pentoxide]], {{chem2|N2O5}}, actually consists of nitronium and [[nitrate]] ions, so it is an [[ionic compound]], nitronium nitrate {{chem2|[NO2]+[NO3]−}}, not a [[molecular solid]]. However, dinitrogen pentoxide in [[liquid]] or [[gas]]eous state is [[molecule|molecular]] and does not contain nitronium ions.<ref name=G&E/><ref>{{Cite journal|url=https://aip.scitation.org/doi/10.1063/1.454679|doi = 10.1063/1.454679|title = The equilibrium constant for N2O5⇄NO2+NO3: Absolute determination by direct measurement from 243 to 397 K|year = 1988|last1 = Cantrell|first1 = C. A.|last2 = Davidson|first2 = J. A.|last3 = McDaniel|first3 = A. H.|last4 = Shetter|first4 = R. E.|last5 = Calvert|first5 = J. G.|journal = The Journal of Chemical Physics|volume = 88|issue = 8|pages = 4997–5006}}</ref>

==Related species==
The compounds [[nitryl fluoride]], {{chem2|NO2F}}, and [[nitryl chloride]], {{chem2|NO2Cl}}, are not nitronium salts but molecular compounds, as shown by their low boiling points (−72&nbsp;°C and −6&nbsp;°C respectively) and short nitrogen–halogen bond lengths (N–F 135 pm, N–Cl 184 pm).<ref>[[F. Albert Cotton|F. A. Cotton]] and G.Wilkinson, Advanced Inorganic Chemistry, 5th edition (1988), Wiley, p.333</ref>

Addition of one electron forms the neutral [[nitryl]] [[radical (chemistry)|radical]], {{chem2|NO2•}}; in fact, this is fairly stable and known as the compound [[nitrogen dioxide]].

The related negatively charged species is {{chem2|NO2(−)}}, the [[nitrite]] ion.

==See also==
* [[Nitrosonium]]

==References==
{{reflist}}

{{Nitrogen compounds}}

[[Category:Oxycations]]
[[Category:Nitronium compounds|Nitronium compounds]]
[[Category:Functional groups]]
[[Category:Nitrogen(V) compounds]]