AIIMS 2019 Chemistry Free Radicals MCQ Question
The given free radicals are shown below: (I) CH₃–ĊH–CH₃, (II) (III) ĊH₂–CH(CH₃)₂ (IV) ĊH₂–CH₃ The stability of free radicals is mostly affected by the factors like resonance, hyperconjugation and inductive effect. In compound (II), there is high resonance effect due to which it is highly stable than other three compounds. The effect of hyperconjugation is directly proportional to the number alpha hydrogen. So, compound I has six alpha hydrogen atoms, compound III has one alpha hydrogen atom and compound IV has three alpha hydrogen atoms. Therefore, the order is
II > I > IV > III
I > II > III > IV
IV > III > II > I
III > IV > I > II
Correct Answer
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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