多氯苊化合物分子结构和热力学性质的理论研究

采用密度泛函理论方法,在B3LYP/6-311G**水平上对35个多氯苊化合物的分子几何结构进行了全优化计算,并获得它们在理想气体状态的一些热力学性质参数,研究了这些性质与氯原子数目和位置的关系,根据多氯苊化合物的相对标准生成Gibbs自由能的大小,得到它们的热力学稳定性顺序.结果表明:所有多氯苊分子中除4个氢原子以外的其他原子都在同一平面上.多氯苊最稳定异构体的ΔfHθ及ΔfGθ随Cl原子数目增加而发生的变化与最不稳定异构体不同.具有相同数目氯原子的多氯苊异构体的ΔfHθ和ΔfGθ与氯原子的取代位置有很大的关系,其相对热力学稳定性主要由分子内的处在不同六元环上的邻近Cl…Cl核排斥作用决定.

Theoretical Studies on the Molecular Structures and Thermodynamic Properties of Polychlorinated Acenaphthene Compounds

Molecular geometric structures of 35 polychlorinated acenaphthene(PCACE) compounds were calculated using density functional theory(DFT) at the B3LYP/6-311G** level and some thermodynamic properties of them in the ideal gas state were obtained.The relations of these thermodynamic properties with the number and position of chlorine atoms were also explored.The stability order of PCACE compounds was obtained according to the magnitude of the relative standard Gibbs free energy of formation(Δr,fGθ).The results shown that all atoms are in the same plane for all PCACE isomers except four H atoms.The change of ΔfHθ and ΔfGθ of the most stable PCACE isomers with increasing the number of chlorine atoms is different from that in least stable PCACE congeners.The values of ΔfHθ and ΔfGθ for PCACE isomers with the same number of chlorine atoms showed a strong dependence on the position of chlorine atoms and the relative thermodynamic stability of PCACE congeners was determined mainly by intramolecular adjacent Cl…Cl nuclear repulsive interaction between Cl atoms at two different six-membered rings.