Reactivity in Relation to Structure

Mayo and Walling draw the following conclusions from their tabulation (Table XX)  

The effects of 1-substituents in increasing the reactivity of monomers towards attacking radicals are in the order, —Cells —CH=CH2  

The above order of reactivity can be correlated with the stabilization 

As a result, the radical is stabilized to the extent of about 20 kcal. Two structures of nearly equal energies can be written for the allyl radical resulting from the addition of butadiene  

The amount of the resonance stabilization is similar to that for the benzyl radical. In radicals formed from monomers having C=0 or C=N groups conjugated with the carbon-carbon double bonds, the corresponding resonance structures 

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