Nitrogen NMR Criteria of Structure

Because of the sensitivity of nitrogen shielding (and coupling constants) to the presence of a lone pair on nitrogen, and to 77-delocalization, useful criteria of structure can be formulated  

Mc2NN0 relative to NNO). Intermediate shielding is observed for intermediate MNO angles (cf. also the deshielding of nitrosyl N if an iV-nitrosamine is distorted from planarity ). Bent nitrogen is less deshielded in aza-arenes and azoles, and quite highly shielded in azides.  

Thus nitrogen NMR can monitor reactions in which the shift of a -electron pair onto nitrogen, as it bends, allows the metal to accept an incoming ligand (and the nitrogen to coordinate a proton or other Lewis acid). A comparable -electron pair shift onto nitrogen is also possible in imido and nitrido ligands.  

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