Stability of free radicals can be explained by
1. Inductive effect : Since free radicals are electron deficient species, presence of electron releasing groups will have a stabilizing effect on them. And the stability order will be,
Tertiary > secondary > primary > CH3
2. Hyperconjugation: Stability of alkyl free radicals can be explained by the number of contributing structures formed due to hyperconjugation. Since the delocalization is due to the presence of α–hydrogens (H's attached to α – C), more the number of α–hydrogens more contributing structures are formed. Thus the stability order is,
3. Resonance : The stability of allyl and benzyl free radicals can be explained by resonance.
