烯酮与乙烯或乙炔的[2+2]环加成反应机理的从头计算研究

用从头计算法研究了乙烯酮与乙烯(或乙炔)环加成反应机理.所有的几何构型优化都采用能量梯度法(在STO-3G水平上).对过渡态结构都用分析力常数矩阵计算进行了确证。为了得到较好的反应位垒和生成热,在HF/STO-3G结构参数基础上。采用MP2/6-31G和MP3/6-31G作了单点能量计算。计算结果表明,这2个反应都按协同、非同步的方式进行。乙烯酮与乙烯和乙炔环加成反应的活化位垒分别为244.2和294.5kJ/mol。

AB INITIO STUDIES ON THE REACTION MECHANISM OF [2+2] CYCLOADDITION OF KETENE WITH ETHYLENE AND ACETYLENE

The reaction mechanism of thermal cycloaddition of ketene with ethylene (or acetylene) wele studied by using ab initio SCF MO method. The geometries of the reactants, products and transition states were optimized by gradient technique at the level of STO-3G. The transition state structures were further confirmed by calculating the analytical force constant matrix. In order to get better energetics, single point calculations using MP2/6-31G and MP3/6-31G basis sets(based on STO-3G geometries) were also performed. The results of calculation show that the two reactions are concerted unsynchroneous 2s+2a] cycloaddition reactions. The activation barriers of eycloaddition of ketene and ethylene(or acetylene) is 244.2 (or 294.5) kJ/ol(MP2/6-31G results).