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.%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.
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