Ayyob Bakry

The study of tautomerics equilibria is of vital importance as tautomeric compounds reactivity highly depends on the proportion of each tautomer. Herein, the tautomeric equilibrium of the 3-phenyl-2,4-pentanedione was studied theoretically by the b3lyp/6-31+g(d)methods. The effect of four solvents was considered (water, methanol, carbon tetrachloride and Cyclohexane).The tautomeric equilibrium takes place through four-membered ring transition state. The barrier heights energies of the tautomerics equilibria reaction of the transition state with reference to Keto were found to be 31.26, 31.23, 30.84, 30.82 and 30.61 kcal mol-1 in water, methanol, carbon tetrachloride, Cyclohexane and the gas-phase, respectively. Furthermore, the electronics energies differences between the Keto-form and Enol-form were found to be -16.50,-16.55, -17.27, -17.34 and -17.89 kcal mol-1 in the same previous solvents respectively. The DFT calculations revealed that the Keto-form is more stable one in all investigations.