2-羟基吡啶质子转移异构化的理论研究

Theoretical Studies of Proton-transfer Tautomerism of 2-hydroxylpyridine

采用量子化学中的密度泛函理论,在B3LYP/6-311++G**计算水平上,系统考察了在水、氨和甲醇分子辅助下,2-羟基吡啶醇式和酮式结构的质子转移异构化行为.结果表明:其醇式和酮式结构均能稳定存在,但后者在能量上稍占优势.3种分子参与的质子转移反应均是按照协同机理进行的.它们的参与能够大大降低反应能垒,使得在动力学上难以发生的质子转移反应得以进行.其中甲醇的辅助效果最佳,其次为水和氨分子.另外,辅助分子和各种介质的溶剂效应均有利于酮式结构的稳定性,这与有关的研究吻合较好.

With and without the assistance of one water, ammonia, and methanol molecule, the protontransfer tautomerisms of 2-hydroxylpyridine are investigated systematically employing the B3LYP/6-311＋ ＋G＊ ＊ level of theory. Both the keto and hydroxyl form of 2-hydroxylpyridine can exist stably though the keto form is slightly more stable than that of hydroxyl form. All of the proton transfer processes assisted with the water, ammonia, and methanol proceed through the concerted mechanism, since only one transition state is located during the proton transfer processes. The corresponding barrier heights are reduced significantly relative to those without assisted case, making the difficult reactions occur easily. The methanol molecule has the best catalytic effect among the three molecules followed by the water and ammonia molecules. Additionally, the stability of keto form has been further enhanced in the presence of the assisting molecules and solvation effects.