用密度泛函理论(DFT)方法在B3LYP/6-31G*水平上研究了苯甲醛肟与炔丙醇加成反应的微观机制和热力学、动力学行为.结果表明,在苯甲醛肟与炔丙醇加成反应过程中,8个可能反应通道的过渡态中均形成非平面五元环结构,其中苯甲醛肟的Z、E构型特征得到了部分保留,但主要部分的键长、键角均发生了变化,电荷也进行了重新分布.苯甲醛肟以羟基型参与反应的4个反应通道均为吸热反应和热力学非自发过程,它们均具有较高的反应势垒、较慢的反应速率和较小的平衡常数;而以离子型参与反应的四个反应通道均为放热反应和热力学自发过程,它们的反应势垒较低,反应速度较快,平衡常数也较大,故苯甲醛肟应主要以离子型参与反应.炔丙醇的两种取向对应着加成反应的两种产物,反应达到平衡后,3-羟甲基二氢异噁唑为主要产物.
The reaction mechanism, thermodynamic and kinetic behavior of the dipole cycloaddition reaction of benzaldoxime with propinol have been studied by DFT method at B3LYP/6-31G* level. The results show that there are eight reaction channels, corresponding to eight transition states, in the reaction process. The main parts of all transition states are non-planar five-membered ring, in which the geometry of Z-benzaldoxime and E-benzaldoxime is maintained partially, but the bond length, bond angle and charge are all changed. The four reaction channels including hydroxyl-type benzaldoxime are endothermic reaction, thermodynamically non-spontaneous process, but the other four reaction channels including ion-type ben- zaldoxime participation are exothermic reaction and thermodynamically spontaneous process. The latter four reaction channels, which have lower reaction barriers, faster reaction velocities and bigger equilibrium constants than those of the former fours, are the chief reaction channels. Two kinds of products can be obtained in the addition reaction of benzaldoxime with propinol, in which 3-hydroxymethyl-dihydroisoxazol is the main product when reaction equilibrium is reached.