Hyponitrous acid

Hyponitrous acid is a chemical compound with formula or HON=NOH. It is an isomer tautomer of nitramide, H2N−NO2.
Hyponitrous acid forms two series of salts, the hyponitrites containing the [ON=NO]2− anion, and the "acid hyponitrites" containing the [HON=NO]− anion.
Structure and properties.
There are two possible structures of hyponitrous acid, "trans" and "cis". "trans"-Hyponitrous acid forms white crystals that are explosive when dry. In aqueous solution, it is a weak acid (p"K"a1 = 7.21, p"K"a2 = 11.54), and decomposes to nitrous oxide and water with a half life of 16 days at 25 °C at pH 1–3:
Since this reaction is not reversible, should not be considered as the anhydride of .
The "cis" acid is not known, but its sodium salt can be obtained.
Preparation.
Hyponitrous acid ("trans") can be prepared from silver(I) hyponitrite and anhydrous HCl in ether:
Spectroscopic data indicate a "trans" configuration for the resulting acid.
Biological aspects.
In enzymology, a hyponitrite reductase is an enzyme that catalyzes the chemical reaction