Resonance in allyl

The stability of a radical depends on the rate of its disappearance or formation according to the reaction conditions. The thermodynamic stability of a radical is related to the ease of dissociation of the R-H bond to give R and H or the R-H dissociation energy. The thermodynamic stability of a radical depends on double bond conjugation and electron delocalization stabilized by resonance in allylic systems produced by hydrogen abstraction in polyunsaturated lipids (see Chapter 2). 

---