Question

Peroxide effect is observed with the addition of HBr but not with the addition of HI to unsymmetrical alkene because

• A. H-I bond is stronger that H-Br and is not cleaved by the free radical
• B. H-I bond is weaker than H-Br bond so that iodine free radicals combine to form iodine molecules
• C. Bond strength of HI and HBr are same but free radicals are formed in HBr
• D. All of these

Answer 1

The Correct Option is B

Let's evaluate each option:

(A) H-I bond is stronger than H-Br and is not cleaved by the free radical: This is incorrect. The H-I bond is weaker than the H-Br bond and can be easily cleaved by free radicals.

(B) H-I bond is weaker than H-Br bond so that iodine free radicals combine to form iodine molecules: This is correct. The H-I bond is weaker, so iodine free radicals are formed and tend to combine to form iodine molecules, preventing the peroxide effect with HI.

(C) Bond strength of HI and HBr are the same but free radicals are formed in HBr: This is incorrect. The bond strength of H-I is weaker than H-Br, and it is this weaker bond that makes free radical formation easier in HBr.

(D) All of these: This is not correct as Option A and Option C are incorrect.
 

The correct answer is (B) : H-I bond is weaker than H-Br bond so that iodine free radicals combine to form iodine molecules.