The reaction of catalytic epoxidation of cyclohexene molecule over the manganese porphyrin has been studied by the DFT methods. Parallel and perpendicular mutual orientations of reacting species have been considered leading to eight different reaction paths, with the cyclohexene, species approaching the catalyst oxo-group from above and from the side of the porphyrin plane (at three different heights). Three possible positions in which the cyclobexene molecule may physisorb on the catalyst have been found. Results of calculations indicate that the formation of the epoxide may occur when the cyclohexene molecule approaches the catalyst oxo-group from above in a parallel orientation. (C) 2004 Elsevier B.V. All rights reserved.