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.

Key words: isomerization, proton transfer, water-assistance