Dienophile Activation Energy, kcal/mol Reaction Energy, kcal/mol
Ethylene +15.29 -55.18
Maleic anhydride +2.18 -53.12
Cyclobutenone +7.45 -56.15
Table 1: Energetics of the Diels-Alder reactions of ethylene, maleic anhydride and cyclobutenone with 1,3-butadiene.