论1-吡啶-3-[4-(苯基偶氮)苯基]-三氮烯的三氮异构化

DFT theoretical study on the isomerization of 1-pyridine-3-[4-phenylazopheny]-triazene

采用3种不同泛函(B3LYP,BP86,PBE1PBE)在6-31G*和6-311+G*基组下,计算有机材料1-吡啶-3-[4-(苯基偶氮)苯基]-三氮烯(PYPAPT)不同结构上三氮异构化的途径有2种可能:(a)分子内质子迁移,(b)水助质子迁移,因此获得它们的互变异构过程活化能、活化吉布斯自由能和质子转移反应的速率常数等性质。采用PCM法研究反应体系的溶剂化效应。证明孤立分子和一水合物最稳定的异构体相同都为M11,计算结果也与实验值符合得很好,溶剂化效应对异构化能垒的影响较大。最稳定的异构体分子内质子转移的速控步骤的活化能为170.48kJ/mol,速率常数为3.86×10-15s-1;当水分子参与反应以双质子转移机理异构化时,活化能显著降低,有利于三氮异构化,其最稳定异构体的速控步骤的活化能为47.41kJ/mol,速率常数为9.73×104s-1。计算结果还表明,氢键作用在增大PYPAPT一水合物相对稳定性、降低质子转移异构化反应活化能等方面起着重要作用。

The isomerization of 1-pyridine-3-[4-phenylazopheny]-triazene（PYPAPT）was studied by density functional theory at B3LYP/6-31G＊,BP86/6-311＋G^＊,PBE1PBE/6-311＋G^＊level.The two possible reaction pathways：（a）intramolecular proton transfer;（b）water-assisted intermolecular transfer were investigated.The reaction activation energies,activation free energies and the rate constants of tautomerism were obtained.The mechanisms of the tautomerization in water solution have been investigated at the same level by SCRF calculations using the PCM model.Calculated results indicate that the M11 structure is always dominant both in the gas phase and aqueous solution,and our calculated the relative energies（ER）are in good agreement with the available experimental values.The solvent effects on the tautomerization reactions of PYPAPT observed by the PCM model did significantly alter the barrier height.The activation energy needed in the minimum structure（a）is 170.48 kJ/mol and the rate constant is 3.86×10^-15s^-1.In water catalysis（b）,double proton transfer was found and the activation energies were dramatically decreased,is 47.41 kJ/mol and the rate constant is 9.73×10^4 s^-1.It was also found that the effect of hydrogen bonds has had an important in pact on increasing the stabilities of monohydrated tautomers and lowering the activation energies.