Acidities of stable simple enols and bond dissociation enthalpies of their H-O bonds in DMSO

The PKHA values for eight stable enols and the oxidation potentials of their anions, E-OX(A(-)), were determined in DMSO, and the bond dissociation enthalpies (BDE) of their O-H bonds were estimated using the equation, BDEHA = 1.37pK(HA) + 23.1E(OX)(A(-)) + 73.3 kcal/mol (1). For Mes(2)C=C-(OH)R enols the PKHA's increase with the bulk of R from 17.8 for R = H to 19.9 for R = t-Bu; the E-OX(A(-)) values become more negative, and the BDEs decrease from 82.2 kcal/mol for R = H to 78.3 for R = t-Bu. The PKHA values roughly parallel the association constants of the enols with the DMSO solvent. These values are discussed in terms of steric and electronic effects.