多溴苊化合物的分子结构和热力学性质

多溴苊是一类潜在的有机污染物。本文采用密度泛函理论在B3LYP/6-311G**水平上优化35个多溴苊化合物的分子几何结构,并获得它们在理想气态的一些热力学性质的数值,研究这些性质与取代的溴原子数目和位置的关系,根据各异构体的标准生成Gibbs自由能的相对大小,求得它们的热力学稳定性顺序。计算结果表明:在大部分多溴苊分子中,除4个氢原子外的其他原子在同一平面上。多溴苊最稳定及最不稳定异构体的ΔfH及ΔfG,都随Br原子数目增加而逐渐增加。溴原子数目相同的多溴苊异构体的ΔfH和ΔfG与溴原子的取代位置有很大的关系,其相对稳定性主要由分子内的处在不同六元环上的邻近Br...Br核排斥作用决定。所有多溴苊化合物在热力学上都比其母体化合物苊相对较难形成。

Molecular structures and thermodynamic properties of polybrominated acenaphthene compounds

Polybrominated acenaphthene(PBACE) compounds are one type of latent chemical pollutants.In this article,molecular geometric structures of 35 PBACE compounds were optimized using density functional theory(DFT) at the B3LYP/6-311G** level and some thermodynamic properties of them in the ideal gas state were calculated.The relations of these thermodynamic properties with the number and position of bromine atoms were also explored,from which the relative stability of PBACE congeners was theoretically proposed according to the magnitude of the relative standard Gibbs free energy of formation(Δ r,f G).The computed results show that atoms other than four H are in the same plane in most PBACE isomers.The values of Δ f H and Δ f G of both most stable and least stable PBACE isomers increase with increasing the number of bromine atoms.The values of Δ f H and Δ f G for PBACE isomers with the same number of bromine atoms show a strong dependence on the position of bromine atoms and the relative stability of PBACE congeners are mainly determined by intramolecular adjacent Br...Br nuclear repulsive interaction between Br atoms at two different six-membered rings.All of PBACE congeners are more difficult to form thermodynamically than their parent compound.