1. Using the values for the resonance energies of benzene and naphthalene given above, explain why Diels-Alder reactions of anthracene take place at the center ring, not one of the end rings. REACTION OF ANTHRACENE WITH MALEIC ANHYDRIDE The Diels-Alder reaction in this experiment uses an unusual cyclic diene-the central ring of anthracene. Benzene and naphthalene do not take part in typical Diels-Alder reactions, because the -electrons of the diene are part of an aromatic ring; if cycloaddition were to occur the aromaticity of that ring would be lost. In anthracene, however, as you will find if you try to draw Kekule resonance structures, all thrse rings cannot be benzenoid simultaneously, so the resonance energy per ring is lower than that of benzene and naphthalene (resonance energies: benzene, 36kcal/mole; naphthalene, 60kcal/mole; anthracene, 84kcal/mole ). Diels-Alder addition across the center ring of anthracene leaves two intact benzene rings in the adduct. and do not take part in usual Diels-Alder reactions. benzene naphthalene