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+){{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}}
|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−1 mol−1
}}
}}
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}}).{{Greenwood&Earnshaw2nd}}
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 equilibrium:
:{{chem2|H2SO4 + HNO3 → HSO4− + [NO2]+ + H2O}}
Structure
The nitronium ion is 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.{{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 }}
Salts
A few stable nitronium salts with anions of weak 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 hexafluoroantimonate {{chem2|[NO2]+[SbF6]-}}. These are all very hygroscopic compounds.{{cite book |title= Aromatic nitration |author= Kenneth Schofield |publisher= CUP Archive |year= 1980 |isbn= 0-521-23362-3 |page= 88 }}
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 gaseous state is molecular and does not contain nitronium ions.{{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|url-access = subscription}}
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 °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, {{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
References
{{reflist}}
{{Nitrogen compounds}}