In chemistry, hyponitrite may refer to the anion ([ON=NO]<sup>2âÂÂ</sup>), or to any ionic compound that contains it. In organic chemistry, it may also refer to the group âÂÂOâÂÂN=NâÂÂOâÂÂ, or any organic compound with the generic formula R<sup>1</sup>âÂÂOâÂÂN=NâÂÂOâÂÂR<sup>2</sup>, where R<sup>1</sup> and R<sup>2</sup> are organic groups. Such compounds can be viewed as salts and esters of hyponitrous acid. An acid hyponitrite is an ionic compound with the anion ([HON=NO]<sup>âÂÂ</sup>).
Hyponitrite exhibits cisâÂÂtrans isomerism.
The trans (E) form is generally found in hyponitrite salts such as sodium hyponitrite () and silver(I) hyponitrite ().
The cis (Z) form of sodium hyponitrite can be obtained too, but it is more reactive than the trans form. The cis hyponitrite anion is nearly planar and almost symmetric, with lengths of about 140 pm for NâÂÂO bond and 120 pm for the NâÂÂN bond, and OâÂÂNâÂÂN angles of about 119ð.
The hyponitrite ions can act as a bidentate ligand in either bridging or chelating mode. There is a bridging cis-hyponitrite group in the red dinuclear form of nitrosyl pentammine cobalt(III) chloride, [Co(NH<sub>3</sub>)<sub>5</sub>NO]Cl<sub>2</sub>.
Hyponitrite can reduce elemental iodine to hydroiodic acid:
Organic trans-hyponitrites R<sup>1</sup>âÂÂOâÂÂN=NâÂÂOâÂÂR<sup>2</sup> can be obtained by reacting trans silver(I) hyponitrite with various alkyl halides. For example, reaction with tert-butyl chloride yields trans di-tert-butyl hyponitrite.
Other alkyl radicals reported in the literature include ethyl, and benzyl. These compounds can be a source of alkoxyl radicals.
Other nitrogen oxyanions include