邻苯二酚烷基化反应机理的密度泛函研究

DFT Study of Pyrocatechol Alykation Reaction Mechanics

采用密度泛函理论(DFT)B3LYP方法,在6-311G(d,p)基组下研究邻苯二酚与N-羟甲基丙烯酰胺的烷基化反应机理,对反应物、过渡态、中间体和产物进行了结构全优化和确认,通过HOMO轨道百分组成预测芳环上的反应活性位点。结果表明:邻苯二酚与N-羟甲基丙烯酰胺烷基化反应机理分四步,活化能分别是61.07、39.69、44.31和31.51J/mol。一取代反应势垒为61.07kJ/mol;二取代反应势垒为44.31kJ/mol。表明二取代反应较一取代更容易发生。另外,一取代产物芳环上活性位点碳原子所带负电荷(-0.806)高于反应物邻苯二酚芳环上的碳原子(-0.124),有利于亲电试剂进攻,说明反应更易发生二取代,这与实验结果一致。

When capsaicin derivatives were synthesized from the alykation reaction of Binary phenol and N-methylolacryamide,as the ratio of Pyrocatechol to N-methylolacryamide changed,it was found that products were only dialkylation.The structures of reactants,transition states,intermediates and products were optimized by using DFT B3LYP/6-311G（d,p）.The frequency,energies and charges were also analyzed.The calculated results show that the reaction includes four steps.The activation energies（Ea）of the four steps are 61.07kJ/mol、39.69kJ/mol、44.31kJ/mol and 31.51kJ/mol respectively.The whole reaction is exothermic except that the electrophilic attack step is endothermic.The reaction energy barrier of the dialkyl reaction is 44.31kJ/mol,lower than 61.07kJ/mol of monoalkyl reaction.In addition,the Mulliken charge datas show that the mulliken charge of the active atom increases after the pyrocatechol being substituted.As a result it is easier to be attacked by the positive ion.