The stabilization energies by interconjugations at the transition states in various Diels-Alder reactions were calculated. It has been found that the stabilization energies are inversely proportional to resonance energies of isolated molecules of polyene and heterocyclic system before reactions. It has been noted that the resonance energies of dienes are smaller than those of dienophiles in two different molecules. Therefore, the possibility of charge-transfer from dienes to dienophiles is hinted