Search

The conformational and structural stabilities of nitrosoethylene CH2=CH–N=O, chloronitrosoethylene CH2=CCl–N=O, and Dichloronitrosoethylene CCl2=CH–N=O were investigated by ab initio Moeller–Plesset perturbation theory of second order (MP2) calculations using the 6−311+G** basis set to include electron correlation. From the calculations all three were predicted to exist predominantly in the planar trans structure (C=C and N=O bonds are trans to each other) with high trans-cis rotational barriers of about 9 kcal mol−1 as a result of pronounced conjugation between C=C and N=O bonds. The vibrational frequencies were computed for the three molecules, and also the d1 and d2 deuterated variants for the parent molecule at the MP2 level. Normal coordinate analyses were carried out and the potential energy distributions (PED), among the symmetry coordinates of the normal modes of the molecule were computed. Complete vibrational assignments were made on the basis of normal coordinate analyses for the molecules. The two chlorinated derivatives of nitrosoethylene were also investigated in the same way. As expected, we then find high Raman and infrared intensities in all modes that contain a high content of chlorine movements because vibrations of C–Cl bonds lead to large changes in polarizability, as well as to a large change in dipole moment. However, modes involving double bonds also have quite large intensities. An appreciable number of modes in these molecules are more or less pure symmetry coordinates. [ABSTRACT FROM AUTHOR]

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]

Abstract The structural stability of halocarbonyl azides CXO-NNN (X=F, Cl and Br) was investigated by DFT and MP2 calculations using the 6-311++G** basis set. From the calculations, the molecules were found to have an s-cis⇔s-trans conformational equilibrium with cis being the lower-energy form. Full energy optimizations were carried out for the transition states and the minima at the B3LYP/6-311++G** and MP2/6-311++G** levels, from which the rotational barriers were calculated to be of the order 8-10 kcal mol-1. The vibrational frequencies were computed at the DFT-B3LYP level and the vibrational assignments for the normal modes of the stable conformers were made on the basis of normal coordinate calculations. [ABSTRACT FROM AUTHOR]