Which free radical is more stable, allyl free radical or benzyl free radical? Can someone pls tell me which one is it? Benzyl free radical has 4 resonance structures compared to allyl free radical which has only 2. More the resonance structures should mean more stable the radical.


But in the book I am referring it is written that free radical stability depends on bond dissociation energy.


According to this Allyl free radical should be more stable but according to resonance structures Benzyl free radical should be stable. Which one is correct?
Yes, generally more resonance structures mean more stability but this case is an exception.

In three of the four resonance structures of the benzyl radical, the aromaticity is being broken which makes then less stable whereas in the allyl radical both the canonical forms are stable.

Therefore the allyl radical is more stable than the benzyl radical.