Resonance Energy - Practice Questions & MCQ

Resonance Enthalpy: 

The theoretical difference in molecular energy between a resonance hybrid and the 'most stable' resonance contributor (if this resonance contributor existed as a real molecule). In other words, the stability gain by electron delocalization due to resonance versus the absence of such delocalization. The resonance energy of benzene is 36 kcal mol^-1 .

Calculation of Resonance Energy:

(1) Resonance energy can be calculated in terms of the heat of the formation data:

Resonance Energy $=\Delta_{\mathrm{f}} \mathrm{H}_{\text {theoretical }}^{\circ}-\Delta_{\mathrm{f}} \mathrm{H}_{\text {actual }}^{\circ}$

(2) Resonance energy can be calculated in terms of the heat of combustion data:

Resonance Energy $=\Delta_c \mathrm{H}_{\text {actual }}^{\circ}-\Delta_c \mathrm{H}_{\text {theoretical }}^{\circ}$

(3) Resonance energy can be calculated in terms of the heat of hydrogenation data:

Resonance Energy $=\Delta_{\text {hydrogenation }} \mathrm{H}_{\text {actual }}^{\circ}-\Delta_{\text {hydrogenation }} \mathrm{H}_{\text {theoretical }}^{\circ}$

Note: Resonance Energy is always a Positive Number. Use this fact to quickly calculate Resonance Energy using the above formulae.

The calculation of Resonance energy in terms of Heat of hydrogenation is given below: