The enthalpy of hydrogenation of but-1-ene to butane is -127 kJ mol^-1 and that of buta-1,3-diene to butane (2 mol H2) is -239 kJ mol^-1. The stabilisation energy of buta-1,3-diene due to conjugation (resonance energy) is:

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The enthalpy of hydrogenation of but-1-ene to butane is $- 127 kJ mo l^{- 1}$ and that of buta-1,3-diene to butane (2 mol $H X_{2}$ ) is $- 239 kJ mo l^{- 1}$ . The stabilisation energy of buta-1,3-diene due to conjugation (resonance energy) is:

Without conjugation, the diene would release about

2 \times 127 = 254

kJ/mol. The observed value is 239 kJ/mol, so the stabilisation is

254 - 239 = 15

kJ/mol.