Question

Which of the following is the most stable free radical?

• A. $C_{6}H_{5}-CH_{2}-CH_{2}^{\cdot}$
• B. $C_{6}H_{5}-CH^{\cdot}-CH_{3}$
• C. $CH_{3}-CH^{\cdot}-CH_{3}$
• D. $C_{6}H_{5}-CH_{2}-CH_{2}-CH_{2}^{\cdot}$

Hint:

Benzylic radicals > Alkyl radicals due to resonance stabilization.

Answer 1

The Correct Option is B

Step 1: Concept
Stability of free radicals depends on resonance and hyperconjugation.
Step 2: Analysis of Option B
The radical $C_{6}H_{5}-CH^{\bullet}-CH_{3}$ is a secondary benzylic radical. It is stabilized by: 1. Resonance with the benzene ring. 2. Hyperconjugation with the methyl group.
Step 3: Comparison
Primary radicals (A, D) and secondary alkyl radicals (C) lack the extensive resonance stabilization provided by a benzene ring directly attached to the radical center.
Step 4: Conclusion
Option (B) is the most stable.
Final Answer:(B)