Nitrens are molecular fragments with six electrons on the nitrogen which are formed thermally or photochemically from hydrazoic acid or organic azides. Kinetics of the cleavage of azides, spectroscopic data, and electron spin resonance measurements constitute proof for a biradical nature of the nitrens studied. As a result of hydrogen shifts, nitrens are capable of isomerization to mines, of hydrogen abstraction from neighbouring molecules affording primary amines, and of ring formation by internal dehydrogenation (insertion reactions). Isomerization and hydrogen shifts are observed primarily with alkylnitrens; however, under favorable structural conditions, hydrogen shifts in arylnitrenes also lead to immines. Arylinitrens dimirize to azo compounds and undergo intra‐ and intermolecular reactions with nucleophilic reactants. Thus, both stable and unstable acylnitrenes, which are formed thermally or photolytically from acyl azides, add on, for example, to dimethyl sulfide or dimethyl sulfoxide, affording sulfimines or sulfoximines, respectively. Nucleophilic reagents, such as alcohols and amines, also react with nitrenes. Besides azides, anil‐N‐oxides also undergo cleavage to give nitrenes. The reaction of N‐chloramines and hydroxylamine‐O‐sulfonic acids with nucleophilic reagents probably does not proceed via a nitrene intermediate, but rathr by an SN mechanism.
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