Nitronium ion
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Systematic IUPAC name
Dioxidonitrogen(1+)
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| Identifiers | |||
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3D model (Jmol)
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PubChem CID
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| Properties | |||
| NO+ 2 |
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| Molar mass | 46.01 g·mol−1 | ||
| Thermochemistry | |||
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Std molar
entropy (S |
233.86 J K−1 mol−1 | ||
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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The nitronium ion, NO+
2, is a cation. It is an onium ion because of its tetravalent nitrogen atom and +1 charge, similar in that regard to ammonium. It is created by the removal of an electron from the paramagnetic nitrogen dioxide molecule, or the protonation of nitric acid (with removal of H2O).
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:
A few stable nitronium salts with anions of weak nucleophilicity can be isolated. These include nitronium perchlorate (NO+
2ClO−
4), nitronium tetrafluoroborate (NO+
2BF−
4), nitronium hexafluorophosphate (NO+
2PF−
6), nitronium hexafluoroarsenate (NO+
2AsF−
6), and nitronium hexafluoroantimonate (NO+
2SbF−
6). These are all very hygroscopic compounds.
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