With di- and triatomic molecules Upon condensing to a liquid,<unk>  dimerizes to dinitrogen dioxide, but the association is weak and reversible. The N–N distance in crystalline NO is 218 pm, nearly twice the N–O distance. Since the heat of formation of •NO is endothermic, NO can be decomposed to the elements. Catalytic converters in cars exploit this reaction: : 2 NO → O2 + N2 When exposed to oxygen,<unk>  converts into nitrogen dioxide: : 2 NO + O2 → 2 NO2 This reaction is thought to occur via the intermediates ONOO• and the red compound ONOONO. In water,<unk>  reacts with oxygen to form nitrous acid (HNO2). The reaction is thought to proceed via the following stoichiometry: : 4 NO + O2 + 2 H2O → 4 HNO2<unk>  reacts with fluorine, chlorine, and bromine to form the nitrosyl halides, such as nitrosyl chloride: : 2 NO + Cl2 → 2 NOCl With NO2, also a radical, NO combines to form the intensely blue dinitrogen trioxide: : NO + NO2 ON−NO2 Organic chemistry The addition of a<unk>  moiety to another molecule is often referred to as nitrosylation. The Traube reaction is the addition of a two equivalents of<unk>  onto an enolate, giving a diazeniumdiolate (also called a nitrosohydroxylamine). The product can undergo a subsequent retro-aldol reaction, giving an overall process similar to the haloform reaction. For example,<unk>  reacts with acetone and an alkoxide to form a diazeniumdiolate on each α position, with subsequent loss of methyl acetate as a by-product: : Traube reaction This reaction, which was discovered around 1898, remains of interest in<unk>  prodrug research.<unk>  can also react directly with sodium methoxide, ultimately forming sodium formate and nitrous<unk>  by way of an N-methoxydiazeniumdiolate. Coordination complexes<unk>  reacts with transition metals to give complexes called metal nitrosyls. The most common bonding mode of<unk>  is the terminal linear type (M−NO). Alternatively,<unk>  can serve as a one-electron pseudohalide. In such complexes, the M−N−O group is characterized by an angle between 120° and 140°. The NO group can also bridge between metal centers through the nitrogen atom in a variety of geometries.
Nitric oxide
Leukotriene
Histamine
Serotonin
Acetylcholine
Interleukin
Nitrosamine
Prostaglandin