3-羰基吡唑质子转移过程的理论研究

采用密度泛函B3LYP／6—311G^＊＊方法，对3-羰基吡唑几何构型进行了全自由度优化，获得了它们的几何结构和电子结构．计算并考察了3-羰基吡唑的两种构象即syn和anti构象的稳定性以及3-羰基吡唑进行结构互变的质子转移过程的四种可能途径：（a）分子内质子转移；（b）水助质子转移；（C）同种二聚体双质子转移；（d）异种二聚体双质子转移．计算结果表明3-羰基吡唑的syn构象中N2-H型的稳定性大于N1-H型，进行质子转移时途径（C）所需要的活化能最小（52．78kJ／mol），途径（a）所需要的活化能最大（200．59kJ／mol）；3，羰基吡唑的。anti构象中N1-H型的稳定性大于N2-H型，进行质子转移时途径（d）所需要的活化能最小（61．09kJ／mol），途径（a）所需要的活化能最大（204．15kJ／mol）．

Theoretical Study on the Proton Transfer in 3-Aldehyde Pyrazole

The molecular structures of 3-aldehyde-pyrazole tautomers with full geometry optimization were calculated by the B3LYP method at the 6-311G** level.The geometry and electronic structures of the tautomers of 3-aldehyde pyrazole and their transition states were obtained.The four possible reaction pathways were investigated including:(a) intramolecular proton transfer;(b) water-assisted intermolecular transfer;(c) isomerization by doubleproton transfer in the dimer and(d) intermolecular proton transfer via the complex formed.The results of the calculation indicated that the N1-H form of the anti conformer was more stable than that of the N2-H form,and the process in(d) has the lowest activation energy(61.09 kJ/mol),whereas the N2-H form of the syn conformer is more stable than that of the N1-H form and the process in(c) has the lowest activation energy(52.78 kJ/mol).It was likely that the hydrogen bonds formed in the complexes played an important role in proton transfer processes in the latter three reaction pathways.