多氯代菲分子结构和热力学性质的密度泛函理论研究

采用密度泛函理论方法在B3LYP/6-311G(d, p)水平上对527个多氯代菲分子的几何结构进行了全优化并计算得到它们的热力学性质(等容热容( )、熵(S$)、标准生成焓(ΔfH$)和标准生成Gibbs自由能(ΔfG$)), 研究了这些性质与取代的氯原子数目和位置的关系, 根据各异构体的相对标准生成Gibbs自由能(Δr,fG$)的大小, 得到它们的热力学稳定性顺序. 计算结果表明: 绝大多数多氯代菲分子具有非平面的几何构型, 在多氯代菲分子中存在三种类型的分子内弱相互作用(H…H、C—H…Cl和Cl…Cl相互作用), 随着分子中取代的氯原子数目的增加, 多氯代菲最稳定异构体的ΔfH$和ΔfG$开始时逐渐减小, 然后又快速增加. 具有相同数目氯原子的多氯代菲异构体的ΔfH$和ΔfG$与氯原子的取代位置有很大的关系. 多氯代菲异构体的相对热力学稳定性主要由分子内的离域π键和Cl…Cl核排斥作用的强弱决定.

Density Functional Theory Studies on the Molecular Structures and Thermodynamic Properties of Polychlorinated Phenanthrenes

Geometric molecular structures of 527 polychlorinated phenanthrenes (PCPhen) have been optimized using density functional theory (DFT) at the B3LYP/6-311G(d, p) level and their thermodynamic properties in the ideal gas state, such as heat capacity at constant volume ( ), entropy (S$), standard enthalpy of formation (ΔfH$) and standard Gibbs free energy of formation (ΔfG$), have been computed. The relations of , S$, ΔfH$ and ΔfG$ with the number and position of chlorine atoms have also been explored, from which the relative stability of PCPhen congeners was theoretically proposed according to the magnitude of the relative standard Gibbs free energy of formation (Δr,fG$). It was found that most of PCPhen isomers are in a nonplanar configuration, with three kinds of intramolecular weak interactions, i.e., H…H, C—H…Cl and Cl…Cl interactions. With increasing the number of chlorine atoms, the values of ΔfH$ and ΔfG$ of the most stable PCPhen isomers decrease initially and then increase quickly. The values of ΔfH$ and ΔfG$ of PCPhen congeners with the same number of chlorine atoms show a strong dependence on the positions of chlorine atoms. The relative thermodynamic stability of PCPhen isomers is determined mainly by relative magnitude of intramolecularly delocalized p bond and Cl…Cl nuclear repulsive interaction.