Question:
Which of the following is correct order of stability of free radicals?
Which of the following is correct order of stability of free radicals?
Updated On: Feb 24, 2026
- allyl > 3° > 2° > 1° > CH3°
- 3° > 2° > 1° > allyl > CH3°
- CH3° > 3° > 2° > 1° > allyl
- 3° > 2° > 1° > CH3° > allyl
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The Correct Option is A
Solution and Explanation
The stability of free radicals is an important concept in organic chemistry. Let's analyze the stability order of various free radicals presented in the options.
- Allyl Radical: The allyl radical (“allyl”) is highly stabilized due to resonance. It is an extended conjugation system which can delocalize the unpaired electron over adjacent carbon atoms, leading to enhanced stability.
- Tertiary Free Radical (3°): These radicals are stabilized through hyperconjugation and inductive effects. Here, the unpaired electron on the carbon is stabilized by electron-releasing alkyl groups, making it more stable than secondary and primary radicals.
- Secondary Free Radical (2°): These radicals are less stable than tertiary but more stable than primary radicals, due to fewer hyperconjugative structures and inductive effects than tertiary radicals.
- Primary Free Radical (1°): These radicals have even less hyperconjugation and inductive effects to stabilize the radical, making them less stable than secondary and tertiary radicals.
- Methyl Radical (CH3°): This is the least stable due to the absence of hyperconjugation and inductive stabilization.
Now, putting these concepts together, the correct order of stability for these free radicals is:
allyl > 3° > 2° > 1° > CH3°
This order reflects the increasing stabilization mechanisms such as resonance, hyperconjugation, and inductive effect that influence free radical stability.
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