ENERGETICS OF ACETIC-ACID ENOL IN AQUEOUS-SOLUTION - A NEW METHOD FORTHERMODYNAMIC ESTIMATION

A new disproportionation calculation allows the estimation of the free energy of formation of the enol of acetic acid as 65 +/- 2 kcal/mol. The value of pK(E) derived from this free energy, pK(E) = 21 +/- 2, is in satisfactory agreement with information from the literature about rates of exchange. Analysis of the data on rates of exchange of the C- H protons of acetic acid using Marcus theory allows an independent est imate of the enol content. Exchange in acid and in base lead to intern ally consistent estimates, pK(E) = 19.3 +/- 2.2, which are within the combined uncertainties of the values from the thermodynamic estimate.