The Diels-Alder reaction of hexachlorocyclopentadiene with norbornadiene gives aldrin but theoretically three other diastereofacial isomers are possible. On oxidation these isomers can generate eight adducts one of which is known as dieldrin. All these, as well as the corresponding reactions with hexafluorocyclopenadiene were studied by semiempirical (AM1 and PM3) and hybrid density functional (B3LYP) methods. Besides the energy levels, the transition states were calculated for the reactions leading to the diastereofacial isomers of aldrin, which indicate that aldrin is the favored product of the reaction both from thermodynamic and kinetic point of view.