Free energy relationships via tautomerism in para-acetophenone derivatives

Computational and Theoretical Chemistry 976 (2011) 88–93

Hossein Tavakol

Abstract

recent years. In present work, the equilibrium and rate constants of keto–enol tautomerism in acetophenone derivatives were calculated using density functional theory. From these calculations, molecular parameters, natural atomic charges and equilibrium and rate constants for tautomeric interconversions were calculated. The results show linear relations between log(Keq/KeqH) (logarithmic ratio of equilibrium constants) and rp, rR or R values. Moreover, the same relations between log(k/kH) (logarithmic ratio
of rate constants) and rp, rR or R values were found in the gas phase and five different solvents. The best correlation was observed when rp values were used as substituent constants. The other diagrams using rm, r+, r, rI, rþ m or F as substituent constants were not shown acceptable regressions or appropriate correlation coefficient. The diagrams of log(Keq/KeqH) (versus substituent constants) showed positive slopes (q) while diagrams of log(k/kH) showed negative slopes. In other words, by the increase of electron-withdrawing property of para-substituent, the equilibrium constant increases while the rate constant decreases.