环氧氯丙烷与亲核试剂反应先开环再分子内环化原因分析  

Analysis of the Reasons for the Reaction of Chloromethyloxirane and Nucleophiles Mainly Undergo the Nucleophilic Ring Opening and Intramolecular Cyclization

作　　者：许家喜 麻远[2] XU Jia-Xi;MA Yuan(College of Chemistry,Beijing University of Chemical Technology,Beijing 100029,China;Department of Chemistry,Tsinghua University,Beijing 100084,China)

机构地区：[1]北京化工大学化学学院,北京100029 [2]清华大学化学系,北京100084

出　　处：《化学教育（中英文）》2024年第16期105-107,共3页Chinese Journal of Chemical Education

基　　金：有机化学本科育人团队项目;有机化学和中级有机化学一流课程建设项目。

摘　　要：亲核试剂与一级卤代烷通常是发生双分子亲核取代反应。而环氧氯丙烷与亲核试剂的反应主要是通过亲核试剂先对其环氧乙烷部分的亲核开环,然后再分子内环化得到反应产物;而不是亲核试剂直接取代环氧氯丙烷的氯原子得到最终产物。其原因是形成小环化合物的香蕉键不是轴向重叠,重叠效果不好,因此,其稳定性比轴向重叠形成的σ键弱。从而,亲核试剂先与环氧乙烷中的弱C—Oσ键进行开环反应,生成的烷氧基负离子再进行分子内的亲核取代环化,得到最终产物。本文通过对反应物中关键化学键的形成轨道和稳定性的分析,合理地解释了环氧氯丙烷与普通一级卤代烷反应性的差别,加深了学生的理解。Nucleophiles and primary haloalkanes generally take place bimolecular nucleophilic substitution.However,the reaction of chloromethyloxirane(epichlorohydrin)and nucleophiles first undergoes a nucleophilic ring opening of its oxirane followed by an intramolecular nucleophilic cyclization,affording final products,rather than nucleophiles directly displace its chlorine atom to give the final products.The reason is that the banana bond for the formation of small ring compounds does not overlap axially.The overlap is not efficient so that the stability of the banana bond is weaker than that of the axially overlapped bond in other compounds.Thus,nucleophiles first attack the weaker C-O o-bond in oxiranes,the generated alkoxides further undergo an intramolecular nucleophilic cyclization,affording the final products.The reactive differences of chloromethyloxirane and primary haloalkanes are rationally explained through analysis of the forming orbitals and stabilities of the crucial chemical bonds in reactants.It would provide a deeper understanding for students.

关 键 词：环氧氯丙烷 亲核取代 亲核试剂 小环化合物 成键轨道 

分 类 号：O621.25-4[理学—有机化学] G642[理学—化学]