2-羟基吡啶质子转移过程的理论研究

采用量子化学中的密度泛函理论,在B3LYP/6-31G(d)基组水平上,计算并考察了2-羟基吡啶分子醇式结构和酮式结构进行结构互变的质子转移过程中的4种可能途径:(a)分子内质子转移,(b)水助催化质子转移,(c)同种二聚体双质子转移和(d)异种二聚体间双质子转移.计算结果表明,途经c所需要的活化能最小(2.6 kJ•mol－1,逆反应则为27.1 kJ•mol－1),而过程a所需要的活化能最大(137.2 kJ•mol－1),途径b和d的活化能居中间(分别为38.7和17.3 kJ•mol－1).研究还表明,氢键在降低反应活化能方面起着重要的作用.

A Theoretical Study on the Proton Transfer in 2-hydroxy Pyridine

The processes of the proton transfer between 2-hydroxy pyridine (Hy) and 2(1H)-pyridone (Py) were investigated by using density functional theory of quantum chemistry method at B3LYP/6-31G(d) level. The four possible reaction pathways: (a) intramolecular proton transfer;(b) water-assisted intermolecular transfer; (c) isomerization by double-proton transfer in the dimer and (d) intermolecular proton transfer via the complex formed by Hy and Py were investigated in the present paper. The calculated results showed that the processes in (b),(c) and (d) has lower activation energies than that of the intramolecular tautomeric oxo-hydroxy reaction (a) because of the formation of hydrogen-bonded complexes in (b),(c) and (d).The activation energies corrected by scaled zero-point vibrational energies for the four reaction processes calculated at the B3LYP/6-31G(d) level are 137.2,38.7,2.6 and 17.3 kJ•mol－1,respectively.It is likely that the hydrogen bonds formed in the complexes play an important role in proton transfer processes in the later three reaction pathways.