Conformational and vibrational analyses for 2,2-dihalovinyl azides CX ₂=CH-NNN (X is F and CI)

The conformational behavior of 2,2-dihalovinyl aizdes CX ₂=CH-NNN (X is F and CI) were investigated by DFT-B3LYP and ab initio MP2 calculations with 6-311++G** basis set. The two molecules were predicted to exist predominantly in the trans (the vinyl CX ₂=CH- and the azide -NNN groups are trans to each other) conformation. The relative energy between cis and trans were calculated to decrease in the order: dichloride > difluoride. Full optimization was performed at the ground and transition states in the molecules at both MP2 and B3LYP levels. The barrier to internal rotation around the C-N single bond was calculated to be 3.719 and 5.171 kcal/mol in the difluoride and the dichloride, respectively. The vibrational frequencies were computed at the DFT-B3LYP level and the calculated infrared and Raman spectra of the cis-trans mixture of the two molecules were plotted. Complete vibrational assignments were made on the basis of normal coordinate calculations for both stable conformers of the two molecules.