Nitrilimines or nitrile amides are a class of organic compounds sharing a common functional group with the general structure R\sCN\sNR corresponding to the conjugate base of an amine bonded to the N-terminus of a nitrile. The dominant structure for the parent compound nitrilimine is that of the propargyl-like in scheme 1 with a C–N triple bond and with a formal positive charge on nitrogen and two lone pairs and a formal negative charge on the terminal nitrogen. Other structures such as hypervalent , allene-like , allylic and carbene are of lesser relevance.
\ce{H-\!{\equiv}}{\color{Blue}\ce{N+}}\!{-}\!{\color{Red}\ce{N-}}\!{-}\!{\color{Red}\ce H} | H-\!{\equiv}N=N-H | \ce H\!{-}\!{\color{Red} \ce{C-}}\!{=}{\color{Blue}\ce{N+}}\!\ce{=N-H} | \ce H\!{-}\!{\color{Blue} \ce{C+}}\!\ce{=N}\!{-}\!{\color{Red}\ce{N-}}\!\ce{-H} | H-C{:}\!-N=N-H |
Nitrilimines were first observed in the thermal decomposition of 2-tetrazoles releasing nitrogen:[1]
Nitrilimines are linear 1,3-dipoles represented by structures and . A major use is in heterocyclic synthesis. E.g. with alkynes they generate pyrazoles in a 1,3-dipolar cycloaddition. Due to their high energy, they are usually generated in situ as a reactive intermediate.
References
- ^ Huisgen, Rolf; Seidel, Michael; Sauer, Juergen; McFarland, James; Wallbillich, Guenter (June 1959). "Communications: The Formation of Nitrile Imines in the Thermal Breakdown of 2,5-Disubstituted Tetrazoles". The Journal of Organic Chemistry. 24 (6): 892–893. doi:10.1021/jo01088a034