The conformational preferences of 1,3-dioxole and 1,3-dioxolane are explained on the basis of the QTAIM electron density analysis of B3LYP/6-311++ G(2d, 2p) electron distributions, supporting the interpretation of the anomeric effect previously proposed by Vila and Mosquera [14]. Thus, distances from methylenic hydrogens to oxygen lone pairs and H-C-O-lp dihedral angles sufficiently explain the atomic population and energy variations, thereby explaining the ring puckering preference. (C) 2010 Elsevier B.V. All rights reserved.