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Experimental and Theoretical Investigation of the Pyrolysis Products of Iminodiacetonitrile, (NCCH2)2NH

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journal contribution
posted on 20.11.2014 by Osman I. Osman
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.