β-丙醇酸内酯气相热分解反应的过渡态——从头计算法研究

本文用量子化学从头计算法研究了β-丙醇酸内酯热分解反应的机理。对均相热分解的两种可能方式进行了自洽场分子轨道法研究(3-21G基组):C_2H_4+CO_2(1)←CH_2—C—O—CH_2→(2)CH_2=C=O+H_2CO反应物、产物和过渡态的几何构型分别用能量梯度法进行了优化, 并对能量做了二级微扰能(MP2)的校正。用这种方法得出反应(1)的活化势垒为166.0 kJ mol~(-1), 反应(2)的话化势垒为302.0 kJ mol~(-1)。计算结果表明: 在一般温度下, 热分解反应主要以反应(1)的机理进行。这个结论与动力学的实验结果是一致的。

THE TRANSITION STATE OF THE GAS PHASE PYROLYSIS OF β-PROPIOLACTONE

The reaction mechanism of the homogeneous prolysis of β-propiolactone (3-oxetanone) was studied by means of ab initio SCF MO method with 3-2lG basis set. There are two possible reaction channels:C_2H_4+CO_2(1)←CH_2—C—O—CH_2→(2)CH_2=C=O+H_2COThe geometries of the reactant, transition states and products of (1) and (2) have been optiminzed by energy gradient technique. Second order Mφller-Plesset perturbation (MP2) calculations were carried out at the HF optimized geometries to obtain better energetics. The activation barriers are 116.0 and 302.0 kJ mol~(-1) for (1) and (2) respectively. From the results of calculations it can be seen that pyrolysis must chiefly proceed via the reaction path (1). This conclusion is in accordance with experimental observations.