中文摘要：

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143．8kJ·mol^-1，水助催化时，反应的活化自由能为38．9kJ·mol^-1，二聚体双质子转移的活化自由能为0．6kJ·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．

英文摘要：

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 k J·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.