稠环芳烃基态及激发态亲核反应活性的量化研究

The quantum research on the nucleophilic reaction activity of polycyclic aromatic hydrocarbons for the ground and excited states

采用量子化学限制性Hartree Fock方法(RHF)和多参考态组态相互作用方法(MRCI),对渺位缩合和迫位缩合稠环芳烃的基态和激发态的最高活性碳位进行了研究。前线轨道的能级研究表明,基态时随着环数的增加,渺位缩合稠环芳烃的前线轨道能级差从1065 kJ/mol逐渐减小到976.4 kJ/mol,说明随着环数的增加,渺位缩合稠环芳烃分子的稳定性逐渐降低,分子反应活性逐渐增强。而迫位缩合稠环芳烃由于分子内部芳香环的结合程度和碳原子的共用程度不一致导致处于基态时前线轨道能极差并没有随着芳环数的增加呈现出线性行为。进一步,通过比较C原子的Mulliken电荷,以及不同位置C-C键的键级和键长研究了稠环芳烃的亲核加氢反应的最高活性碳位。结果表明,处于基态时,渺位缩合稠环芳烃的最高活性碳位出现在内侧芳环的外侧碳位上,而迫位缩合稠环芳烃的最高活性的碳位出现在外侧芳环的外碳位置;处于激发态时,大多数渺位缩合、迫位缩合稠环芳烃的最高活性碳位与基态是重合的,部分稠环芳烃的最高活性碳位会发生转移。

Using the restricted Hartree Fock （RHF） and Multi Reference Configuration Interaction （MRCI） method, we studied the most reactive carbon atoms on the cam-condensed and peri-condensed polycyclic aromatic hydrocarbons （PAHs） in the ground states and the excited states respectively. With the increasing of the aromatic rings, the energy gap of the HOMO-LUMO in the cam-condensed PAHs decreases from 1065 kJ/mol to 976.4 kJ/mol in the ground states. It means that the stability and the molecular reactivity of the cata-condensed PAHs＇ are decreasing with the increasing of the aromatic tings number. However, for the peri-condensed PAHs, the dependence presents a nonlinear behavior of HOMO-LUMO gap with the aromatic rings increasing, due to the degree of integration of the inner aromatic rings in peri-condensed PAHs is so different from cam-condensed PAHs, and the degree of carbon atoms on the inner rings are also shared differently. In order to identify the most reactive carbon atoms, the Mulliken charges and the Mayer＇s bond orders were calculated as the criterion. The results demonstrated that the most reactive carbon atoms appeared at the outer C locations in the inner benzene rings for cam-condensed PAHs, while for peri-condensed PAHs they were the outer C in the outer benzene rings in the ground states. And in their low-lying excited state, most C locations of cata-condensed and peri-condensed PAHs didn＇t shift, only a few of them shifted.