Infrared and Raman spectra and vibrational analyses calculated with Moeller–Plesset perturbation theory of second order of nitrosoethylene and its chloro-derivatives

Abstract

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.