Ab initio and density functional theoretical studies of structures and vibrational spectra of simple silanimines

The structural stability of 1-vinylsilanimine CH₂=CHSiH=NH, silanimine-1-carboxaldehyde OHCSiH=NH and its carboxylic acid fluoride derivative OFCSiH=NH was investigated using ab initio calculations. The calculations were carried out at the DFT-B3LYP/6-311 ++ G**, MP2/6-311 ++ G** and HF/6-311 ++ G** levels. From the calculations the molecules were predicted to exist predominantly in the trans conformation. 1-Vinylsilanimine was predicted to exist predominantly in the trans conformation with high trans-cis rotational barrier. The barrier to internal rotation around the C-Si single bond in 1-vinylsilanimine was calculated at DFT-B3LYP/6-311 + + G** level to be of a bout 5.6 kcal/mol, while that in silanimine-1-carboxaldehyde to be of about 4.4 kcal/mol. However, replacing the aldehydic H atom with F atom further decreases the barrier to a value of 2.9 kcal/mol. The vibrational frequencies were computed at DFT-B3LYP level of theory. Normal coordinate calculations were carried out and potential energy distributions were calculated for the stable conformers of the molecules.