【摘要】 为了探索2-(2-羟基苯亚甲基胺)-4,6-二羟基-嘧啶(M1)分子醇式和酮式结构互变异构化的反应机理, 利用密度泛函理论(DFT)方法, 在B3LYP/6-311+G(d, p)基组水平上, 对M1化合物异构化反应的势能面进行了研究, 在探讨各种可能的反应途径中, 发现单体至少有8种异构体和10种过渡态. 结果表明: 2-(2-羟基苯亚甲基胺)-6-羟基-4(3H)嘧啶酮(M6)不论是单体、与水形成的配合物, 还是二聚体, 比其相对应的异构体能量低, 表明在通常情况下是以M6形式稳定存在的; 在考察的可能反应途径中, 直接进行的分子内质子转移过程需要的活化自由能为143.8 kJ·mol-1, 水助催化时, 反应的活化自由能为38.9 kJ·mol-1, 二聚体双质子转移的活化自由能为0.6 kJ·mol-1, 二聚体双质子转移所需活化自由能最低, 在室温下就可以进行, 由此可见氢键在降低反应活化能方面起着重要的作用.更多还原

【Abstract】 To determine the tautomerism mechanism between the enol form and the keto form of 2-(2-hydroxybenzylidenamino)pyrimidine-4,6-diol(M1) the potential energy surface of the isomerization was studied using density functional theory(DFT) calculations at the B3LYP/6-311+G(d,p) level.We found that there were at least 8 isomers and 10 transition states in the possible reaction pathways.All the possible processes of the reaction were studied.The results showed that the energy of 6-hydroxy-2-(2-hydroxybenzylideneamino) pyrimidine-4(3H)-one(M6) was lower than those of the other isomers in the form of a monomer,a hydrate,and a dimer.Therefore,it was the most stable isomer.In these possible reaction pathways the activation free energy required for intramolecular prototropy was 143.8 kJ·mol-1 and for the proton transfer process that was catalyzed by water was 38.9 kJ·mol-1.The activation free energy in the double-proton transfer of the dimer was 0.6 kJ·mol-1,which was the lowest value.The latter pathway was feasible at room temperature.This implies that hydrogen bonding plays an important role in depressing the activation energy of the reaction.更多还原