Resonance Energy Heat of hydrogenation for trans-1,3- pentadiene is less than expected. ·△Hfor1-pentene is30.0kcal/mol and for trans-2-pentene is 27.4 kcal/mol,so expect 57.4 kcal for trans-1,3-pentadiene. ·Actual△His53.7kcal,so the conjugated diene is more stable. Difference,(57.4-53.7)3.7 kcal/mol,is the resonance energy. => Chaper 15 3 Chaper 15 3 Resonance Energy • Heat of hydrogenation for trans-1,3- pentadiene is less than expected. • H for 1-pentene is 30.0 kcal/mol and for trans-2-pentene is 27.4 kcal/mol, so expect 57.4 kcal for trans-1,3-pentadiene. • Actual H is 53.7 kcal, so the conjugated diene is more stable. • Difference, (57.4 – 53.7) 3.7 kcal/mol, is the resonance energy. =>