Various quantum chemical methods, including Hartree-Fock (HF), density functional (DFT/B3LY-P), Moller-Plesset perturbation (MP2), and coupled-cluster [CCSD, CCSD(T), CC3] schemes, have been exploited with correlation-consistent basis sets in an attempt to resolve controversies surrounding the equilibrium structure of ground-state acetylacetone. Geometry optimizations performed at the CCSD(T)/aug-cc-pVDZ level of theory predict a global minimum-energy configuration of C-s symmetry that exhibits an interoxygen distance of 2.575 angstrom, with the symmetric (C-2v) transition state for proton transfer presenting a potential barrier of 1276.7 cm(-1) height. The resulting theoretical description of acetylacetone is in excellent agreement with recent electron diffraction experiments. (c) 2006 Elsevier B.V. All rights reserved.