Resonance Energy
The extra stability a molecule gains from electron delocalisation, measured against the most stable single Lewis structure.
Formula / equation
ΔE_res = E(hybrid) − E(best structure)
Unit
kJ/mol
In depth
It is determined experimentally by comparing a measured enthalpy of hydrogenation or combustion with the value predicted for a localised structure. A large resonance energy explains kinetic sluggishness: benzene resists addition because doing so would destroy its delocalisation.
Examples in the real world
Benzene's resonance energy is about 150 kJ/mol, the gap between its measured and predicted hydrogenation enthalpies.