Conformational stability and vibrational analyses of vinyl diazene CH2CH-NNH and vinyl imine CH2CH-CHNH

The conformational and structural stability of vinyl diazene and vinyl imine were investigated by DFT-B3LYP and ab initio MP2 calculations with 6-311+G** basis set. Vinyl diazene was predicted to exist only in the planar trans-anti conformation (CCNN and CNNH dihedral angles are 180°), while vinyl imine to exist in two trans (CCCN dihedral angle is 180°) conformations. The trans-anti (CCNH dihedral angles is 180°) conformation of vinyl imine was predicted to be about 1 kcal/mol lower in energy than the trans-syn (CCNH dihedral angles is 0°) form that is in excellent agreement with an earlier microwave results. The vibrational frequencies were computed at the DFT-B3LYP level and the calculated infrared and Raman spectra of each molecule were plotted. Complete vibrational assignments were made on the basis of normal coordinate calculations for the two molecules.