聚偏二氯乙烯构象分布的理论研究

在MP2/6-311++G**水平下, 对2,2,4,4-四氯戊烷与2,2,4,4,6,6-六氯庚烷旋转异构体构象进行几何优化和能量计算. 结果表明, 对于2,2,4,4-四氯戊烷, 采用gauche-gauche排列的旋转异构体的能量较低; 2,2,4,4,6,6-六氯庚烷旋转异构体中, 采用trans-gauche-trans-gauche排列的构象能量较低. 反之, 完全采用trans-trans排列的旋转异构体构象能量较高, 不稳定. 通过比较模型分子不同旋转异构体构象的能量差值可以得到一级和二级特征的相互作用能差, 进而计算统计权重参数. 在此基础上, 应用计算得到的模型分子的几何构型与统计权重参数, 分别构建针对—CH2—和—CCl2—中心的聚偏二氯乙烯的6态旋转异构态模型. 通过旋转异构态模型可以计算聚偏二氯乙烯分子中各种构象的分布.

Theoretical Studies on Conformational Distribution of Poly(vinylidene choloride)

Geometries and energies of various low-energy conformers of the stereoisomers of 2,2,4,4-tetrachloropentane and 2,2,4,4,6,6-hexachloroheptane were determined at the MP2 level with a 6-311 G** basis set.For 2,2,4,4-tetrachloropentane,the energy of the conformer with gauche-gauche arrangement is lower;For 2,2,4,4,6,6-hexachloroheptane,the conformer with trans-gauche-trans-gauche arrangement is stable.In contrast,the conformer with trans-trans arrangement is unstable and the energy is higher.Based on the quantum calculations,the first- and second-order characteristic interaction can be obtained by comparing the energies among different conformers of the stereoisomers which are used to determine the statistical weight parameters in a rotational isomeric state model.According to the geometries of the conformers and the statistical weight parameters,we can construct six-state statistical weight matrices.Furthermore,the populations of CH2 and CCl2 centered dihedral pairs in poly(vinylidene chloride) are determined from the quantum chemistry based rotational isomeric state model.