The processes of the proton transfer between various tautomers of allopurinol were investigated by using density functional theory method at B3LYP/6-311+G(d,p)level in the gas and aqueous phases.The three possible rea...The processes of the proton transfer between various tautomers of allopurinol were investigated by using density functional theory method at B3LYP/6-311+G(d,p)level in the gas and aqueous phases.The three possible reaction pathways:(a)intramolecular proton transfer;(b)water-assisted proton transfer;(c)tautomerization by double-proton transfer in the dimer were investigated in the present paper.The calculated results showed that the processes in(b)and(c)has lower activation energies than that of the intramolecular tautomeric reaction(a)because of the formation of hydrogen-bonded complexes in(b)and(c).It implied that the hydrogen bonds formed in the complexes played an important role in proton transfer processes in the later two reaction pathways.展开更多
采用密度泛函理论,在B3LYP/6-31++G//B3LYP/6-31G基组水平上对5-甲基胞嘧啶互变异构体及质子转移机理进行了研究,获得了10种5-甲基胞嘧啶互变异构体及12个异构化过渡态,并获得了互变异构过程的反应焓、活化能、活化吉布斯自由能和质子...采用密度泛函理论,在B3LYP/6-31++G//B3LYP/6-31G基组水平上对5-甲基胞嘧啶互变异构体及质子转移机理进行了研究,获得了10种5-甲基胞嘧啶互变异构体及12个异构化过渡态,并获得了互变异构过程的反应焓、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,5-甲基胞嘧啶各互变异构体的相对热力学稳定性为:M1>M3>M4>M5>M6>M2>M7>M8>M9>M10。其中氨-酮式结构M1能量最低,稳定性最高;亚氨-烯醇式结构M10相对能量最高,稳定性最低。在5-甲基胞嘧啶的异构化过程中,部分异构体之间可以相互转化,其中键旋转较质子迁移所需活化能较低,反应较易实现。由氨酮式M1通过分子内质子迁移及键旋转异构转化共有6条反应通道,其主通道(5)速控步骤的活化能为163.81 k J·mol^(-1),反应较难实现。展开更多
PM3 method has been applied to study the tautomeric reactions of p-R-phenyltetrazoIes. The results obtained show that these tautomeric reactions are all endother mic.The activation energies of the tautomeric reactions...PM3 method has been applied to study the tautomeric reactions of p-R-phenyltetrazoIes. The results obtained show that these tautomeric reactions are all endother mic.The activation energies of the tautomeric reactions are 234.101(H), 234.311(CH3), 233-599(CI) and 232.031(NO2) kJ.mol-1, respectively. The reaction has higher activation energy when R is an electron-donating group,and has lower activation energy when R is an electron-attracting group.展开更多
文摘The processes of the proton transfer between various tautomers of allopurinol were investigated by using density functional theory method at B3LYP/6-311+G(d,p)level in the gas and aqueous phases.The three possible reaction pathways:(a)intramolecular proton transfer;(b)water-assisted proton transfer;(c)tautomerization by double-proton transfer in the dimer were investigated in the present paper.The calculated results showed that the processes in(b)and(c)has lower activation energies than that of the intramolecular tautomeric reaction(a)because of the formation of hydrogen-bonded complexes in(b)and(c).It implied that the hydrogen bonds formed in the complexes played an important role in proton transfer processes in the later two reaction pathways.
文摘采用密度泛函理论,在B3LYP/6-31++G//B3LYP/6-31G基组水平上对5-甲基胞嘧啶互变异构体及质子转移机理进行了研究,获得了10种5-甲基胞嘧啶互变异构体及12个异构化过渡态,并获得了互变异构过程的反应焓、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,5-甲基胞嘧啶各互变异构体的相对热力学稳定性为:M1>M3>M4>M5>M6>M2>M7>M8>M9>M10。其中氨-酮式结构M1能量最低,稳定性最高;亚氨-烯醇式结构M10相对能量最高,稳定性最低。在5-甲基胞嘧啶的异构化过程中,部分异构体之间可以相互转化,其中键旋转较质子迁移所需活化能较低,反应较易实现。由氨酮式M1通过分子内质子迁移及键旋转异构转化共有6条反应通道,其主通道(5)速控步骤的活化能为163.81 k J·mol^(-1),反应较难实现。
文摘PM3 method has been applied to study the tautomeric reactions of p-R-phenyltetrazoIes. The results obtained show that these tautomeric reactions are all endother mic.The activation energies of the tautomeric reactions are 234.101(H), 234.311(CH3), 233-599(CI) and 232.031(NO2) kJ.mol-1, respectively. The reaction has higher activation energy when R is an electron-donating group,and has lower activation energy when R is an electron-attracting group.
