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AIIMS2019Chemistry-Organic Chemistry

AIIMS 2019 Chemistry Free Radicals MCQ Question

Type: MCQ-conceptual-Medium-Class 11

Compare stability of free radicals

(I) CH3−C˙H−CH3\text{CH}_3-\dot{\text{C}}\text{H}-\text{CH}_3

(II) C6H5−C˙H2\text{C}_6\text{H}_5-\dot{\text{C}}\text{H}_2

(III)C˙H2−CH(CH3)2(IV) C˙H2−CH3\dot{\text{C}}\text{H}_2-\text{CH}(\text{CH}_3)_2 \qquad \text{(IV) }\dot{\text{C}}\text{H}_2-\text{CH}_3

A

II > I > IV > III

B

I > II > III > IV

C

IV > III > II > I

D

III > IV > I > II

Correct Answer

Option B

Detailed Explanation

Option B is correct because the stability of free radicals is influenced by hyperconjugation and resonance. Compound (II) benefits from significant resonance stabilization, making it the most stable. Compound (I) has six alpha hydrogen atoms, allowing for extensive hyperconjugation, thus ranking second. Compound (IV) has three alpha hydrogens, providing moderate stability, while compound (III) has only one alpha hydrogen, making it the least stable. Other options incorrectly prioritize compounds based on less effective stabilization factors or misinterpret the contributions of hyperconjugation and resonance.

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