The O-H bond homolytic dissociation of water, hydrogen peroxide, methanol, phenol, and cathecol is investigated by density functional theory (DFT) and ab initio coupled cluster calculations. DFT results are based on several recently proposed functionals, including B98, PBE, VSXC, and HCTH. The dependence of DFT results on the basis-set size is discussed using correlation-consistent polarized (cc-pVXZ) basis-sets (X = 2-5). A scheme proposed by Truhlar is used to extrapolate CCSD energies. Basis-set extrapolated CCSD results for the O-H bond homolytic dissociation enthalpies of phenol and cathecol are in excellent agreement with experimental information. (c) 2005 Elsevier B.V. All rights reserved.