The reactions of Fe2＋ with CH3X （X=H, Cl） have been studied by density functional theory method detailedly. The results demonstrated that the H abstraction in Eq. 4 can proceed via the lowest activation barrier （△Ga= 0.23 kcal/mol） in all feasible pathways. However, the mechanisms of oxidative insertion and the SN2 substitution are not competitive because of thermodynamic factors. The electronic structure analysis suggests that the overlap between metal 3d orbital and substrate σc x results in the preference of Fe2＋ front side attack on the C--X bond. This study is expected to shed light on the nature of the title reac-tions and provide theoretical clues and foundation for future research.%采用密度泛函理论（DFT）详尽地研究了Fe2＋与CH3X（X=H,Cl）的反应机理.结果表明在所有通道中,反应4的H提取能垒最低（Ga=0.23 kcal/mol）,氧化插入机制和SN2取代机制没有竞争性.详尽的电子结构分析表明由于金属3d与底物的σ＊C—X可以最好的重叠,从而Fe2＋从前端进攻C—X键有利于反应.该研究揭示了其微观本质,为Fe2＋活化C—X键等相关研究提供理论线索和依据.
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