Li Quan-Song, Fang Wei-Hai, Yu Jian-Guo
Department of Chemistry, Beijing Normal University, Beijing 100875, PR China.
J Phys Chem A. 2005 May 5;109(17):3983-90. doi: 10.1021/jp044498t.
The potential energy profiles for proton-transfer reactions of 2-hydroxypyridine and its complexes with water were determined by MP2, CASSCF and MR-CI calculations with the 6-31G** basis set. The tautomerization reaction between 2-hydroxypyridine (2HP) and 2-pyridone (2PY) does not take place at room temperature because of a barrier of approximately 35 kcal/mol for the ground-state pathway. The water-catalyzed enol-keto tautomerization reactions in the ground state proceed easily through the concerted proton transfer, especially for the two-water complex. The S1 tautomerization between the 2HP and 2PY monomers has a barrier of 18.4 kcal/mol, which is reduced to 5.6 kcal/mol for the one-water complex and 6.4 kcal/mol for the two-water complex. The results reported here predict that the photoinduced tautomerization reaction between the enol and keto forms involves a cyclic transition state having one or two water molecules as a bridge.
采用6-31G**基组，通过MP2、CASSCF和MR-CI计算确定了2-羟基吡啶及其与水的配合物的质子转移反应的势能面。由于基态途径存在约35 kcal/mol的势垒，2-羟基吡啶（2HP）和2-吡啶酮（2PY）之间的互变异构反应在室温下不会发生。基态下的水催化烯醇-酮互变异构反应通过协同质子转移容易进行，特别是对于双水配合物。2HP和2PY单体之间的S1互变异构有18.4 kcal/mol的势垒，对于一水配合物降低到5.6 kcal/mol，对于双水配合物降低到6.4 kcal/mol。此处报道的结果预测，烯醇式和酮式之间的光诱导互变异构反应涉及以一个或两个水分子作为桥的环状过渡态。
