【摘要】 用从头算的方法在6-31G水平上研究了3-羟基-3-甲基-2-丁酮（1）和苯甲酰甲酸甲酯（2）热分解反应的机理.结果是:前一反应是经历五元环过渡态到达氢键中间体,它接着直接分解成乙醛的异构体和丙酮,最后乙醛的异构体异构化成乙醛;后一反应经历六元环过渡态形成中间体1（INT1）,中间体1（INT1）直接分解成中间体2（INT2）和甲醛,中间体2（INT2）经过第二个过渡态分解成苯甲醛的异构体和一氧化碳,最后苯甲醛异构体异构化成苯甲醛.其中氢迁过程是反应的速控步骤.在MP₂/6-3lG//HF/6-31G+ZPE水平上,对应于这两个反应速控步骤的活化位垒分别是251.42kJ/mol和247.94kJ/mol.采用传统过渡态理论计算了两反应的热反应速率常数,理论的计算结果与实验值吻合较好.更多还原

【Abstract】 The mechanism and kinetics for the decomposition of 3-hydroxy-3-methyl-2-butanone and methyl benzoylformate have been studied by using the ab initio RHF/6 - 31G method. The calculated activation barriers of the two reactions are 251.42kJ/mol and 247.94kJ/mol, respectively, which are in reasonable agreement with the experimental data. The calculated results show that the decomposition of two reactions is a concerted process with hydrogen transferring and bond breaking via a five-membered cyclic transition state and a six-membered cyclic transition state, respectively. The thermal rate constants of the two reactions are obtained by calculating microcanonical probability fluxes through transition state, which are fairly accurate, by comparison with the experimental results.更多还原