Jakob Wirz, "Kinetic studies of keto-enol and other tautomeric equilibria by flash photolysis" Advances in Physical Organic Chemistry, Vol 44, 2010, Ch. 6, pp. 325-356.


Abstract: Flash photolysis has provided a wealth of kinetic and thermodynamic data for tautomerization reactions. Equilibrium constants of enolization, KE, spanning a range of 30 orders of magnitude, have thereby been determined accurately as the ratio of the rate constants of enolization, kE, and of ketonization, kK. Nowadays, tautomerization constants KE can be predicted with useful accuracy by performing ab initio or density functional theory calculations. Free energy relationships based on empirical data can then be used to estimate the lifetime of unstable tautomers in wholly aqueous solutions and in aqueous buffers. These studies have uncovered some remarkable findings such as the CH-acidity of 2,4-cyclohexadienone, pKaE = - 2.9, or the unusually high acidities of ethynols and ethynamines. The analysis of these data provides reliable assignments for the elementary reactions that govern tautomerization reactions and how they depend on pH.