Nitroniumion

The nitronium ion ( cation or Nitryl ) NO2 is an unstable under ordinary conditions cation which is formed by removal of an electron from the paramagnetic nitrogen dioxide, or by protonation and subsequent elimination of water from the nitric acid.

Despite its instability, it is versatile in the electrophilic substitution of other, especially organic compounds, is used mainly in the nitration of aromatic compounds. The ion is formed in situ by mixing nitric acid and sulfuric acid. The following reaction takes place:

The nitronium ion continues to exist in solid form dinitrogen pentoxide, N2O5, an ionic solid consisting of nitronium and nitrate ions. The liquid or gaseous forms, however, are always constructed molecular and thus do not contain nitronium. Some nitronium salts with anions of low nucleophilicity, such as Nitroniumtertrafluorborat or Nitroniumperchlorat (NO2 ClO4 - ) can be isolated, but are very reactive.

The nitronium ion is isoelectronic with carbon dioxide and also has a linear structure with an ONO bond angles of 180 °.

Related species

The compounds of nitryl fluoride, NO2F, and nitryl chloride, NO2Cl, no nitronium salts, but molecular weight compounds, such as the low boiling points ( -72 ° C and -6 ° C), and the short lengths of the nitrogen -halogen bond point (NF 135 pm, N -Cl 184 pm ).

The addition of an electron leaves a neutral Nitryl radical arise: • NO2 - a stable and known compound: nitrogen dioxide. This is compatible with its dimer, dinitrogen tetroxide the ( N2O4 ), in a temperature-and pressure-dependent equilibrium. N2O4 is not present as a radical.

The associated negative charged species is NO2, the nitrite ion.