Experimental and theoretical investigation of the pyrolysis products of iminodiacetonitrile, (N≡CCH2)2NH.

The gas-phase FTIR study of the pyrolysis products of iminodiacetonitrile, (N≡CCH2)2NH has revealed the existence of C-cyanomethanimine, N≡CCH═NH, and ketenimine, CH2═C═NH. The former has two isomers: Z and E; while the later readily taumerizes to acetonitrile, CH3C≡N. A trapping/revaporization system has been used to purify C-cyanomethanimine. The analysis of the rotational structures of the IR medium resolution C-type CNH bend, ν6, and C═N torsional mode, ν10, has led to a conformational characterization of these isomers. The Z-isomer was shown to be the major product. This conjecture was supported by ab initio MO calculations that confirmed the relative total energy stability of the Z-isomer over its E-counterpart by 0.173 to 2.326 kJ/mol. The K values indicated that the equilibrium concentration of Z-C-cyanomethanimine amounts to up to three times that of E-C-cyanomethanimine. A further investigation using NBO technique proved the predilection of the Z-isomer. In addition it relates its provenance of preference to the remote nN6 → σ*C4-N5 interaction that stabilized it by 1.10 kcal/mol. A thorough theoretical investigation of the tautomerization reaction between ketenimine and acetonitrile will be published in a separate contribution.