1-(4-硝基苯基)-3-(5,6-二甲基-1,2,4三氮唑)-三氮烯质子迁移的理论研究

采用密度泛函B3LYP在6-31G*基组下,对有机显色剂1-(4-硝基苯基)-3-(5,6-二甲基-1,2,4三氮唑)-三氮烯(NPDMTT)的各种可能结构进行质子迁移的3种可能途径:(a)分子内质子迁移,(b)水助质子迁移,(c)甲醇助质子转移的计算,得到了各种途径异构体的相对能,获得了它们的互变异构过程的活化能、活化吉布斯自由能和质子转移反应的速率常数等性质。计算结果表明,分子内质子转移形成的各种异构体相对能量较大,当水分子或甲醇分子参与反应时,异构体的相对能量明显减小,但无论是孤立分子、一水合物还是一甲醇合物,其最稳定的异构体都相同,均为A2。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在N11和N13间转移的速控步骤的活化能为130.9 kJ.mol-1,反应速度常数为2.172×10-11s-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,其中异构体质子在N11和N13间转移的速控步骤的活化能为22.55 kJ.mol-1,反应速度常数为3.617×107s-1;当醇分子参与反应以双质子转移机理异构时,活化能减小得更多,其中异构体质子在N11和N13间转移的速控步骤的活化能为2.384 kJ.mol-1,反应速度常数为9.032×1011s-1。计算结果还表明,氢键作用在增大NPDMTT一水合物和NPDMTT一甲醇合物相对稳定性、降低质子转移异构化反应活化能等方面起着重要作用。

DFT theoretical study on the isomerization of 1-(4-Nitrophenyl)-3-(5,6-dimethyl-1,2,4-triazol)-triazene

The isomerization of 1-(4-Nitrophenyl)-3-(5,6-Dimethyl-1,2,4-Triazol)-Triazene(NPDMTT) was studied by density functional theory at B3LYP/6-31G* level.The three possible reaction pathways:(a) intramolecular proton transfer;(b) water-assisted intermolecular transfer and(c) methanol-assisted intermolecular transfer were investigated.The relative energies E R,reaction activation energies,activation free energies and the rate constants of tautomerism were obtained.The relative energies of intramolecular proton transfer are the largest,however,the relative energies are significantly reduced in the water-assisted intermolecular transfer and methanol-assisted intermolecular transfer.The results indicate that the A2 structure is always dominant both in the gas phase and aqueous solution.The solvent effects on the tautomerization reactions of NPDMTT observed by the PCM model did significantly alter the barrier height.The activation energy needed in the minimum structure(a) is 130.9 kJ.mol-1 and the rate constant is 2.17×10-11 s-1 ;In water catalysis(b),double proton transfer was found and the activation energies were decreased to 22.55 kJ.mol-1 and the rate constant is 3.618×10 7 s-1 In methanol catalysis(c),double proton transfer was also found and the activation were dramatically decreased to 2.383 kJ.mol-1 and the rate constant is 9.03×10 11 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 monomethylated tautomers or lowering the activation energies.