Using DFT computations (B3LYP and BHandHLYP functionals) with isodesmic reactions as working chemical reactions, and extended basis sets with diffuse functions, the standard enthalpies of formation of an alpha-tocopherol model (where the aliphatic chain and the neighbour methyl group have been changed to hydrogen atoms) and its free radical alpha-tocopheroxy were theoretically estimated for the first time: -79.4 +/- 2.0. and -54.9 +/- 2.0 kcal mol(-1), respectively. These enthalpies of formation correspond to the O-H bond dissociation enthalpy of BDE(O-H) = 76.6 +/- 2.0 kcal mol(-1), in excellent agreement with the gas-phase experimental value for natural a-tocopherol, which lends confidence to the method and model used. (C) 2004 Elsevier B.V. All rights reserved.