Stability of Allylic and Benzylic Radicals
An allylic radical has an unpaired electron on an allylic carbon and, like an allylic cation, has two contributing resonance structures.
A benzylic radical has an unpaired electron on a benzylic carbon and, like a benzylic cation, has five contributing resonance structures.
Because of their delocalized electrons, allyl and benzyl radicals are both more stable than other primary radicals. They are even more stable than tertiary radicals.