Computational study of the keto/enol equilibrium in 2-fluoro-beta-diketones, (R1COCHFCOR2) with R= -CH3, using semi-empirical method AM1

CHED 1379

Maryauri Perez, dawn@coqui.net, Sonia M Velez, dawn@coqui.net, Zuleyka Alvarado, dawn@coqui.net, and Juan G Estevez, dawn@coqui.net. Chemistry, University of Puerto Rico at Cayey, # 205 Ave. Antonio R. Barcelo, Cayey, PR 00736
Given the growth in the fluoride synthesis of a-diketones in the last two decades and the lack of an experimental and computational study to improve our knowledge of the 2-fluoro-a-diketones we have carried out calculations of 16 of these in their keto and enolic forms. The species studied have a common R2 = -CH3 with R1=: -CH3 ,t-bu,CF3, Ph-, 2-FPh-, 2-CH3Ph-, 2-CH3OPh-, 4-FPh-, 4-CH3Ph-, 4-CH3OPh-, 4-NCPh-, 4-O2NPh-, 2-Pyridyl-, 2-Pyrrolyl-, 2-Furyl-, 2-Thienyl-. For the calculations we have used semi-empirical method AM1 in the form of optimization of energy provided in the computational package HyperChem. The results show that the keto form is more stable for most of the cases, with the exception of those species with R1=: -CH3, 2-CH3Ph-, 4-NCPh-, 4-O2NPh-. The difference in energy for the keto-enol equilibrium (enol a= R1- COH2CF-COR2) goes from - 1.610 kcal/mol to 1.987 kcal/mol. The equilibrium between enol a and enol b (R1COCF=COHR2) is discussed.