EQUILIBRIUM ACIDITIES AND HOMOLYTIC BOND-DISSOCIATION ENTHALPIES OF M-SUBSTITUTED AND P-SUBSTITUTED BENZALDOXIMES AND PHENYL METHYL KETOXIMES

The equilibrium acidities in DMSO of nine p-and NI-substituted benzald oximes and eight p-substituted phenyl methyl ketoximes were measured. Estimates of the homolytic bond dissociation energies (BDEs) of the ac idic O-H bonds in these compounds were made by combination of their pK (HA) values with the oxidation potentials of their conjugate bases, E- ox(A(-)), using the equation BDE = 1.37pK(HA) + 23.06E(ox)(A(-)) + 73. 3 kcal (1 kcal = 4.184 KJ). Plots of E-ox(A(-)) vs pK(HA) for p-substi tuted benzaldoximes and p-substituted phenyl methyl ketoximes were lin ear with slopes near unity. Consequently, as required by the above equ ation, the BDEs estimated for the O-H bonds in these oximes were const ant, being 88.3 + 0.3 and 89.2 +/- 0.4 kcal, respectively. (C) 1998 Jo hn Wiley & Sons, Ltd.