Influence of fluorine substitution in nitrosoethylene and their vibrational spectra, calculated with Møller-Plesset perturbation theory of second order
- 作者：Hassan M. Badawi and Wolfgang Fö ; rner
- 关键词：Conformational equilibria ; Normal coordinate analyses ; Rotational barriers ; Fluorinated nitrosoethylenes
- 刊名：Journal of Molecular Structure ; THEOCHEM
- 出版年：2005
- 期刊代码：63_01661280
- 类别：ch
- 出版时间：2005
- 卷：725
- 期：1-3
- 页码：183-189
- 文件大小：158 K
摘要
The conformational and structural stability of monofluoro-nitrosoethylene CH2
CF–NO, and difluoro-nitrosoethylene CF2CH–NO were investigated by ab initio Møller-Plesset Perturbation Theory of second order (MP2) calculations using the 6-311+G** basis set to include electron correlation. From the calculations the two molecules were predicted to exist predominantly in the planar trans structure with high trans–cis rotational barriers of about 10–11 kcal/mol as a result of pronounced conjugation between CC and NO bonds. The differences in the rotational barriers when going from the parent molecule, nitrosoethylene, to its fluorinated derivatives are explained on the basis of electronegativity. The vibrational frequencies were computed for the two molecules 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 molecules were computed. Complete vibrational assignments were made on the basis of normal coordinate analyses for the molecules. As expected we find there low Raman and appreciable infrared intensities in all modes which contain a high content of fluorine movements because vibrations of C–F bonds lead to a small change in polarizability, but to a large change in dipole moment. However, also modes involving double bonds have quite large intensities in both spectra. An appreciable number of modes in these molecules are composed of relatively large numbers of symmetry coordinates, i.e. they are highly mixed.
CF–NO, and difluoro-nitrosoethylene CF2CH–NO were investigated by ab initio Møller-Plesset Perturbation Theory of second order (MP2) calculations using the 6-311+G** basis set to include electron correlation. From the calculations the two molecules were predicted to exist predominantly in the planar trans structure with high trans–cis rotational barriers of about 10–11 kcal/mol as a result of pronounced conjugation between CC and NO bonds. The differences in the rotational barriers when going from the parent molecule, nitrosoethylene, to its fluorinated derivatives are explained on the basis of electronegativity. The vibrational frequencies were computed for the two molecules 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 molecules were computed. Complete vibrational assignments were made on the basis of normal coordinate analyses for the molecules. As expected we find there low Raman and appreciable infrared intensities in all modes which contain a high content of fluorine movements because vibrations of C–F bonds lead to a small change in polarizability, but to a large change in dipole moment. However, also modes involving double bonds have quite large intensities in both spectra. An appreciable number of modes in these molecules are composed of relatively large numbers of symmetry coordinates, i.e. they are highly mixed.© 2004-2018 中国地质图书馆版权所有 京ICP备05064691号 京公网安备11010802017129号 地址：北京市海淀区学院路29号 邮编：100083 电话：办公室：(+86 10)66554848；文献借阅、咨询服务、科技查新：66554700 |