Conformational stability and normal coordinate analyses for 1-halovinyl azides CH 2=CX-NNN (X is F, Cl and Br).

The conformational behavior of 1-halovinyl azides CH ₂=CX?NNN (X=F, Cl and Br) were investigated by DFT-B3LYP and ab initio MP2 calculations with the 6-311++G** basis set. The molecules were predicted to exist predominantly in the trans (the vinyl CH 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 order: bromide>chloride>fluoride. Full optimization was performed at the ground and transition states in the molecule at both MP2 and B3LYP levels. The barrier to internal rotation around the C?N single bond in the three molecules was calculated to be about 4?5 kcal mol ^-1. The vibrational frequencies were computed at the DFT-B3LYP level and the calculated infrared and Raman spectra of the cis? trans mixture of the three molecules were plotted. Complete vibrational assignments were made on the basis of normal coordinate calculations for both stable conformers of the three molecules. [ABSTRACT FROM AUTHOR]