Conformational stability and normal coordinate analyses of imidoylketene O=C=CH-CH=NH

The conformational and structural stability of imidoylketene O=C=CH-CH=NH were investigated by DFT-B3LYP and ab initio MP2 calculations with the 6-311+G** basis set. From the calculations imidoylketene was predicted to exist predominantly in a mixture of trans-anti (the CCCN dihedral angle is 180°) and cis-anti (the CCCN dihedral angle is 0°) conformations with the trans-anti being the lower energy form. The two anti conformations were predicted to have a comparable relative stability with the C-C rotational barrier of about 9-10 kcal/mol at DFT-B3LYP and MP2 calculations. The equilibrium constanat for the trans⇔cis conformational conversion of the two anti forms of imidoylketene was calculated to be 0.4432 kcal/mol that corresponds to an equilibrium mixture of about 31% cis-anti and 69% trans-anti at 300 K. The vibrational frequencies were computed at the DFT-B3LYP level and the infrared and Raman spectra of the molecule were calculated. Complete vibrational assignments were made on the basis of normal coordinate analyses.