Nitroso
Nitroso refers to a functional group in organic chemistry which has the NO group attached to an organic moiety. As such, various nitroso groups can be categorized as C-nitroso compounds (e.g., nitrosoalkanes; R−N=O), S-nitroso compounds (nitrosothiols; RS−N=O), N-nitroso compounds (e.g., nitrosamines, R1N(−R2)−N=O), and O-nitroso compounds (alkyl nitrites; RO−N=O).
Nitrosyls are non-organic compounds containing the NO group, for example directly bound to the metal via the N atom, giving a metal–NO moiety. Alternatively, a nonmetal example is the common reagent nitrosyl chloride (Cl−N=O).
Nitric oxide is a stable radical, having an unpaired electron.
Reduction of nitric oxide gives the hyponitrite anion, NO−:
Oxidation of NO yields the nitrosonium cation, NO+:
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 extreme modes: as NO+ and as NO−. It is generally assumed that 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°. However, the results of many studies have shown that the ionic descriptions of the NO ligand do not correlate with metal–NO geometry. A more realistic description of electron-counting in metal–nitrosyl chemistry is given by the Enemark–Feltham notation.
Nitroso compounds can be prepared by the reduction of nitro compounds or by the oxidation of hydroxylamines. A good example is (CH3)3CNO, known formally as 2-methyl-2-nitrosopropane, or t-BuNO, which is prepared by the following sequence:
(CH3)3CNO is blue and exists in solution in equilibrium with its dimer, which is colorless, m.p. 80–81 °C.
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