The energetic, geometric and electronic differences of the meso and chiral form of oxirane and cyclobutene derivatives have been studied using DFT methods. The partition of several molecular characteristics (energy, charge and volume) into atomic contributions has been carried out within the AIM framework. The energetic analysis shows that the main contribution to the energy differences came from the chiral carbon atom, where the different substituents are attached. The molecular volume differences can be explained based on the results obtained for the substituents in the two dispositions. (c) 2005 Elsevier B.V. All rights reserved.