Pyrolysis of 3-azidopropionitrile studied by UV photoelectron and matrix-isolation IR spectroscopies: Formation of ketenimine H2CCNH

The electronic structure, vibrational properties and pyrolysis behaviour of 3-azidopropionitrile (3APN, N3CH2CH2CN) are investigated using ultraviolet photoelectron spectroscopy (UVPES) and matrix-isolation infrared (IR) spectroscopy, supported by results from ab initio and DFT electronic structure calculations. 3APN is found to have an HOMO vertical ionisation energy (VIE) of 10.05 ± 0.02 eV and the strongest IR absorption bands located at 2173 and 1296 cm−1. Pyrolysis of the title compound revealed the presence of N2, HCN, CH3CN and ketenimine, H2CCNH, among the decomposition products, the latter behaving as a reaction intermediate. From G3 computational results, 3-iminopropionitrile, CNCH2CHNH, was found to be formed in competition with H2CN − CH2CN, through 160–180 kJ mol−1 energy barriers. On the basis of experimental evidence and G3 results, ketenimine is proposed as the dominant intermediate arising from further decomposition of both imine (CNCH2CHNH) and H2CNCH2CN compounds.

► The pyrolysis of 3-azidopropionitrile is studied by UVPES and matrix-isolation IR.
► N2, CH3CN and HCN are detected among the decomposition products.
► Ketenimine is also formed and behaves as a reaction intermediate.
► Conformational selectivity regarding pyrolysis outcome can potentially be foreseen.