多氯联苯醚的结构参数和热力学性质的密度泛函理论研究

采用密度泛函理论(DFT)方法在B3LYP/6-31G*水平上对209个多氯联苯醚(PCDEs)系列化合物进行了全优化和振动分析计算, 得到各分子的结构参数和热力学性质, 并研究了这些参数与氯原子的取代位置及取代数目(N_PCS)之间的关系. 结果表明: 分子平均极化率(α)、焓(H^?)、自由能(G^?)、恒容热容( )和熵(S^?)与N_PCS之间有很强的相关性(相关性系数r²分别为0.9955, 1.0000, 1.0000, 0.9918, 0.9995), 分子体积(V_m)和最高占据轨道能(E_HOMO)与N_PCS也有较好的相关性, 相关性系数r²分别为0.9735和0.9362. 设计等键反应, 计算了PCDEs系列化合物的标准生成热(Δ_fH^?)和标准生成自由能(Δ_fG^?). 根据异构体自由能的相对大小, 从理论上求得异构体的相对稳定性顺序.

DFT Study on the Structural Parameters and Thermodynamic Prop-erties of Polychlorinated Diphenyl Ethers

Fully optimized calculation and frequency analysis of 209 polychlorinated diphenyl ether (PCDE) compounds were carried out using DFT method at the B3LYP/6-31G* level and their structural and thermodynamic parameters were obtained. The relation of these parameters with number and position of Cl atom substitution (N_PCS) was studied and it was found that there existed high correlation between molecular mean polarizability (α), enthalpy (H^?), free energy (G^?), heat capacity at constant volume ( ) or entropy (S^?) and N_PCS (correlative coefficients being 0.9955, 1.0000, 1.0000, 0.9918 or 0.9995 respectively). It was also found that molecular volume (V_m) and the energy of the highest occupied molecular orbital (E_HOMO) have good correlation with N_PCS and correlative coefficients r² were 0.9735 and 0.9362 respectively. The isodesmic reactions were designed to calculate standard enthalpy of formation (Δ_fH^?) and standard free energy of formation (Δ_fG^?) of PCDE congeners. The order of relative stability of PCDE congeners was theoretically proposed based on the relative magnitude of their Δ_fG^?.