Cyclohexadiene bond dissociation energy

The dissociation energy of the first C—H bond in methane is 33 kcal mole-1 greater than that for the weakest C—H bond in the highly reactive 1,4-cyclohexadiene [13] this is equivalent to a rate factor of 1024 at 25°C. The usual correlation between activation energy and bond dissociation energy or reaction enthalpy is found in the form of the Polyani equation... 

Calculate from appropriate bond and stabilization energies the heats of reaction of chlorine with benzene to give (a) chlorobenzene and (b) 1,2-dichloro-3,5-cyclohexadiene. Your answer should indicate that substitution is energetically more favorable than addition. Assume the bond dissociation energy for a C=C it bond to be 6 5 kcal the resonance stabilization energy of benzene to be 36 kcal, and that of 1,2-dichloro-3,5-cyclohexadiene to be 3 kcal. 

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