水助酮和烯醇类化合物互变异构反应机理的理论研究

采用MP2方法研究了水助MeC(＝O)(CH2R)与MeC(OH)(＝CHR)之间的异构化反应, 确定了相应的过渡态结构并计算了反应势垒. 研究结果表明, 常温下MeC(＝O)(CH2R)与MeC(OH)(＝CHR)之间的异构化反应容易通过2个水分子的参与而实现. 研究结果还表明, 发生质子转移的碳原子在过渡态中采取近sp3杂化. 凡是能够稳定该sp3轨道上的孤对电子的取代基, 都将使质子转移反应的势垒降低, 使异构化反应易于进行.

Theoretical Studies on Isomerization Mechanism between Ketone and Enol Compounds Assisted by Water Molecules

Theoretical studies on the isomerization mechanism between ketone and enol compounds MeC(＝O)(CH2R) and MeC(OH)(＝CHR) were carried out with the MP2 method. The optimal structures of ketone, enol, and transition states were located and the reaction barriers were predicted. The calculation results show that among all 14 reactions studied in this paper, the reaction barrier is lowered for the electron withdrawing group and for the group with an unoccupied orbital whereas it is raised for the electron donating group without an unoccupied orbital. The calculation results suggest that the intramolecular process be kinetically unfavorable because the high barrier exists whatever the substituent is. The one water-assisted intermolecular transfer process is less favorable either. The process assisted by two water molecules is the most favorable one because the low barrier exists whatever the substituent is.