Hydrogen oxonitrate(I) Hyponitrous acid monomer Nitronous oxide Nitroxyl (common name) or azanone (IUPAC name)[2] is the chemical compound HNO.

The conjugate base, NO−, nitroxide anion, is the reduced form of nitric oxide (NO) and is isoelectronic with dioxygen.

Nitroxyl is a weak acid, with pKa of about 11, the conjugate base being the triplet state of NO−, sometimes called nitroxide.

[10][11] Nitroxyl rapidly decomposes by a bimolecular pathway to nitrous oxide (k at 298 K = 8×106 M s):[10] The reaction proceeds via dimerization to hyponitrous acid, H2N2O2, which subsequently undergoes dehydration.

[12] Nitroxyl donors, known as nitroso compounds, show potential in the treatment of heart failure and ongoing research is focused on finding new molecules for this task.