二氟亚烷基卡宾与丙酮环加成反应的量化研究

用量子化学的二阶微扰和密度泛函理论研究了单重态二氟亚烷基卡宾和丙酮环加成反应的机理.在MP2/6-31G*和B3LYP/6-31G*基组水平上,优化得到了反应途径上反应物\,过渡态\,中间体和产物的几何构型;计算并考察了5种可能的反应途径,势能面上各驻点的构型参数\,振动频率和能量;通过振动分析对过渡态和中间体构型进行了确认.计算结果表明,二氟亚烷基卡宾与丙酮环加成反应的主要反应通道由3步组成:(1) 两反应物首先生成一富能中间体INT1b,它是一无势垒的放热反应,放出的热量为122.1 kJ/mol;(2) 中间体INT1b经过过渡态TS3a1异构化为另一中间体INT3a,其势垒为14.3 kJ/mol;(3) 中间体INT3a又经过过渡态TS4异构化四元环产物P4,其势垒为4.6 kJ/mol.

Quantum Chemical Study on the Cycloaddition Reaction of Difluoroalkylidenecarbene and Acetone

The mechanism of cycloaddition reactions of singlet difluoroalkylidenecarbene and acetone has been studied using second-order perturbation and density functional theory of quantum chemisty method at MP2/6-31Gand B3LYP/6-31Glevels.The geometrical parameters,harmonic vibrational frequencies and energies of stationary points on the potential enery surface are calculated.The structures of the stationary points are optimized,and the intermediates and transition states are detected by the frequency analysis.The calculated results show that this cycloaddition reaction has five possible reaction pathways.According to the data of the activation energy,we predict the major reaction channel of the cycloaddition reaction of singlet difluoroalkylidenecarbene with acetone,which proceeds in three steps:(1) the two reactants frist form a enery-rich intermediate INT1b,which is an exothermic reaction of 122.1 kJ/mol with no energy barrier,(2) the intermediate INT1b isomerizates to another intermediate INT3a via transition state TS3a1with enery barrier of 14.3 kJ/mol,(3) intermediate INT3a isomerizates to a four-membered ring product(P4) via transtion state TS4 with energy barrier of 4.6 kJ/mol.