Question

Which of the following is the most stable free radical?

• A. \( (C_6H_5)_2\dot{C}H \)
• B. \( \dot{C}H_3 \)
• C. \( (CH_3)_3\dot{C} \)
• D. \( CH_2 = \dot{C}H \)

Hint:

Free radicals stabilized by resonance (especially benzene rings) are more stable than those stabilized only by hyperconjugation.

Answer 1

The Correct Option is A

Step 1: Understand stability of free radicals.
Stability of free radicals depends on resonance and hyperconjugation.
Resonance stabilization is more effective than hyperconjugation.

Step 2: Analyze option (A).
\( (C_6H_5)_2\dot{C}H \) is a diphenylmethyl radical.
The unpaired electron is delocalized over two benzene rings.
This provides extensive resonance stabilization.

Step 3: Analyze option (B).
Methyl radical has no resonance or hyperconjugation.
Thus, it is least stable.

Step 4: Analyze option (C).
Tertiary radical is stabilized by hyperconjugation from three methyl groups.
However, it lacks resonance stabilization.

Step 5: Analyze option (D).
Vinyl radical has very poor stability due to lack of effective resonance stabilization.

Step 6: Compare stability.
Resonance stabilization \( > \) hyperconjugation
Thus, diphenylmethyl radical is most stable.

Step 7: Conclusion.
\[ \boxed{(C_6H_5)_2\dot{C}H} \]