3,6-二羟基哒嗪质子转移过程的理论研究

为了探索 3 ,6 二羟基哒嗪分子醇式和酮式结构互变异构化的反应机理 ,本研究组采用DFTB3LYP/6 3 11+G(d)方法对标题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 ,发现至少有 3 4种异构体和 43种过渡态 .结果表明 ,6 羟基 3 ( 2H) 哒嗪酮不论是单体 ,与水形成配合物 ,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 6 羟基 3 ( 2H) 哒嗪酮形式稳定存在的 ,这与前人通过实验数据对互变异构体的比率进行预测的结果是一致的 ;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能为 14 2 .2kJ·mol-1,水助催化时 ,反应活化能为 41.3kJ·mol-1,考虑溶剂效应后 ,其活化能为 5 9.2kJ·mol-1,二聚体双质子转移的活化能为 16.8kJ·mol-1,二聚体双质子转移所需活化能最低 ,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

Theoretical Study on the Proton Transfer in 3,6-Dihydroxypyridazine

For researching the mechanism of tautomerism between enol form and keto form of 3,6-dihy~droxy~pyri~dazine, the potential energy surface of the isomerization was studied employing DFT at B3LYP/6-311+G(d). It was found that there were at least 34 isomers and 43 transition states in possible reaction pathways. All the possible processes of reaction were studied. The results showed that the energy of 2,3-dihydro-6-hydroxy-pyridazin-3-one is lower than those of other isomers in the form of monomer, hydrate or dimer. So it was the most stable one. It was consistent with the former report that predicted the ratio of isomers by experimental data. In three possible reaction pathways, the activation energy needed by intromolecular prototropy was 142.2 kJ/mol, that by water catalysis proton transfer was 41.3 kJ/mol which became 59.2 kJ/mol after correction with the effect of solvent activation energy and that by double-proton transfer in dimer was 16.8 kJ/mol which was the lowest activation energy. The last pathway was possible at room temperature. It implied that the hydrogen bond played an important role in depressing the activation energy of reaction.