The energetics of formation of heterocomplexed cations formed by asymmetric (OHO)-H-...-O-... hydrogen bonding in systems of pyridine N-oxide and its derivatives was studied by means of restricted Hartree-Fock and Moller-Plesset ab initio calculations. The energy and Gibbs free energies of cationic heteroconjugation were calculated using the 6-31G* basis set in which a d polarization function is accounted for. The calculated energies, DeltaE(BHB+1,) and Gibbs free enthalpies, DeltaG(BHB+1), of formation of the heterocomplexed cations in vacuo have been found to correlate very good with respective calculated energies and Gibbs free energies of protonation of both the proton acceptors (at a fixed pK(a) value of the proton donor) and proton donors (at a fixed basicity of proton acceptor) and slightly worse with experimentally determined cationic heteroconjugation constants (expressed as log KBHB+1) determined on acetonitrile.