Theoretical vibrational spectra and analyses of isocyanatoketene O=C=CH-N=C=O

The conformational stability of isocyanatoketene O=C=CH-N=C=O was investigated by Density Functional B3LYP and ab initio second-oreder Möller Plesset MP2 calculations with the 6-311+G** basis set. Isocyanatoketene was predicted to have the s-cis ⇔ s-trans conformational equilibrium with the s-trans being the predominant form. Full structural optimization was performed at the ground and transition states and the trans-cis barrier was calculated to be about 2kcal/mol. The vibrational frequencies were computed at the DFT-B3LYP level, and the calculated infrared and Raman spectra of the cis-trans mixture were plotted. Vibrational calculations were also done for deuterated d₁-isocyanatoketene. Reliable vibrational assignment was provided on the basis of normal coordinate calculations for the stable conformers of the molecule.