Nitrile ylide
Nitrile ylides also known as nitrilium ylides, or nitrilium methylides are generally reactive intermediates. With a few exceptions, they cannot be isolated. However, a structure has been determined on a particularly stable nitrile ylide by X-ray crystallography. Another nitrile ylide has been captured under cryogenic conditions.
As ylides, they possess a negative charge and a positive charge on adjacent atoms. As a 1,3-dipole, several resonance structures can be drawn (1a–d). The most appropriate resonance structure is dependent upon the substituent pattern (the identity of the R and R′ groups in 1 and 2). The 3-dimensional structure of the nitrilium ylide itself may also provide a clue as to the most appropriate resonance structure, with a linear R–C≡N–C unit supportive of the charge distribution indicated for resonance structures 1a & 1b and also consistent with the nomenclature nitrilium ylide. As resonance structures 1c and 1d become more important the nitrilium ylide distorts its geometry in favor of a different valence tautomer, 2.
Nitrile ylides are isoelectronic with nitrile oxides.
...
Wikipedia