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采用密度泛函理论(DFT)方法,在B3LYP/6-311G**和B3LYP/6-31G*两种水平上,对76种多氟代二苯并对二噁英系列化合物(PFDDs)进行了几何构型的全优化,并计算了各分子在298.15 K,1.013×105 Pa的标准状态下的热力学参数.基组从6-31G*增大到6-311G**没有显著改变标准生成热(ΔfHθ)、标准生成自由能(ΔfGθ)和标准熵(Sθ)数值.根据B3LYP/6-311G**水平计算得到的ΔfGθ的相对大小,求得PFDDs同数目取代氟原子的各异构体的相对稳定性的顺序.采用基团贡献法计算了多溴代二苯并对二噁英(PBDDs)、多氯代二苯并对二噁英(PCDDs)和PFDDs的辛醇-水分配系数(lg Kow).并将PFDDs的ΔfHθ,ΔfGθ,Sθ和lg Kow的计算结果与PBDDs和PCDDs的相关数值进行了比较.同时,计算了PFDDs各组异构体化合物的生成反应相对速率常数,采用统计热力学程序计算了这些化合物在200至1800 K的恒压摩尔热容(Cp,m),并用最小二乘法求得Cp,m与温度之间的相关方程,发现Cp,m与T,T-1和T-2之间有着很好的相关性.
Sixty-six polyfluorinated dibenzo-p-dioxins (PFDDs) were investigated by density functional theory (DFT) at B3LYP / 6-311G ** and B3LYP / 6-31G * Geometry optimization, and calculating the thermodynamic parameters of each molecule under standard conditions of 298.15 K and 1.013 × 10 5 Pa. Increasing the base set from 6-31G * to 6-311G ** did not significantly change the standard heat of formation ΔfHθ), the standard free energy of formation (ΔfGθ), and the standard entropy (Sθ) values were calculated from the relative sizes of ΔfGθ calculated from the B3LYP / 6-311G ** level to determine the relative number of PFDDs to each isomer of the substituted fluorine atom Order of stability.The octanol-water partition coefficient (lg) of polybrominated dibenzodioxins (PBDDs), polychlorinated dibenzo-p-dioxins (PCDDs) and PFDDs Kow), and the calculated results of ΔfHθ, ΔfGθ, Sθ and lg Kow of PFDDs were compared with those of PBDDs and PCDDs, and the relative rate constants of the formation reaction of isomers of PFDDs were calculated. The statistical thermodynamics The program calculates the constant molar heat capacity (Cp, m) for these compounds at 200 to 1800 K and uses the least squares method to find the Cp, m versus temperature The correlation equations, found Cp, m and T, between T-1 and has a T-2 good correlation.