The ground state SCF IMO theory was applied to the Diels-Alder reactions of cyclopentadiene with 2-substituted acrylonitriles. The CNDO/2 MO of the separate systems, including both $sigma$ and $pi$ electrons, was used as starting point. The qualitative prediction of the relative reactivity was made with the calculated primary interaction energies. Here the calculated activation energies appeared to be realistic. The stereoselectivity determined by the calculated secondary interaction energies represented the endo-selectivity for all the substituents. The reason for the slightly unsymmetrical ring closure at the transition state was discussed in terms of valence inactive electron densities of the reacting atoms