Nitrosyl refers to the diatomic species with the formula NO. Nitrosyls are molecules with the general formula RNO, where R represents an unspecified substituent. A common example is nitrosyl chloride, NOCl (although its structure is better represented ONCl).

Nitrosyl also refers to the discrete molecule nitric oxide, NO. Nitric oxide is a stable radical, having an unpaired electron.

Reduction of nitric oxide gives the hyponitrite anion, NO⁻:

NO + e⁻ → NO⁻

Oxidation of NO yields the nitrosonium cation, NO⁺:

NO → NO⁺ + e⁻

Nitrosyl as a ligand

Main article: Metal nitrosyl

Nitric oxide can serve as a ligand in complexes. The resulting complexes are called metal nitrosyls, and can bond to a metal atom in two distinct modes: as NO⁺ and as NO⁻. NO⁺ coordinates linearly, the M−N−O angle being 180°, whereas NO⁻ forms a bent geometry, with an M−N−O angle of approximately 120°.

Nitroso compounds

Main article: Nitroso compound

Nitroso compounds are a class of organic compounds containing the nitroso functional group, R−N=O.