氟、胺取代基对乙烯和甲醛环加成的影响

采用较新的半经验分子轨道方法AM1研究了氟、胺取代基对乙烯和甲醛环加成反应的影响．对三个环加成反应(C_2H_4+COF_2，H_2NHC＝CHNH_2+H_2CO以及H_2NHC＝CHNH_2+COF_2)的研究结果表明：1) 各反应均是经历双自由基中间体的两步过程，而第一步是速度控制步骤；2) 三个反应的活化位垒依次降低；3) 胺取代基比氟取代基对活化势垒的降低作用更为显著。

The Influence of Fluorine or/and Amine Substituents on the Cycloaddition Reaction of Ethylene and Formaldehyde

The influence of fluorine or/and aAnne substituents to the mechainsm of cycloaddition reaction of ethylene and formaldehyde has been studied by using senilemPirical molecular orbital theory UAM1 presented by M. J. S. Dewar et al in 1985,and performed with GAUSSIAN 86 program. Three chendcal reactions (C2H4+COF2,H2NHC= CHNH2 +H2 CO and H2NHC=CHNH2 +COF2 ) have been studied in detail. Thevarious critical points of all the reactions studied have been fully optimized with Berny gradients and transtiton structures have been coallrmed by frequency analysis. From the results we concluded that: 1) All the reaction pathways studied in this work are found toProceed via a two-step approach characterized by diradical gauche intermediates and the rate detedrining step is the first step for all the thIee reactions. 2) The fluoride or/and anilne substituents can all reduce the potential energy barrier of the cycloaddition reaction of ethylene and formaJdehyde, and amine is more favourable than fluoride.