The geometries of the ground and first triplet excited state of malonaldehyde are compared for two distinct configurations of the molecule. The first represents the equilibrium geometry and the second structure corresponds to the transition state for the interamolecular hydrogen transfer. The ground state computations utilize both self-consistent field and Moller–Plesset second-order perturbation theory. The excited state computations employ several different theoretical methods; unrestricted Hartree–Fock (uhf), unrestricted second-order Moller–Plesset perturbation theory (ump2), ci Singles (cis), and complete active space self-consistent field (cas). The geometric parameters obtained for the two configurations are contrasted in both the ground and excited state. The structural differences are related to the extent of hydrogen bonding present, which is compared to the calculated proton transfer barrier.