Sample 1Medium
A reaction scheme shows propene, CH3–CH=CH2, reacting along two arrows: the upper arrow, with HBr alone, gives A; the lower arrow, with HBr in the presence of benzoyl peroxide, gives B. What are A and B?
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The answer is D.
Without peroxide, HBr adds by Markovnikov's rule through the more stable secondary carbocation, giving 2-bromopropane. In the presence of benzoyl peroxide the addition goes by a free-radical path, anti-Markovnikov, giving 1-bromopropane.
- A.
This reverses the two rules: without peroxide addition is Markovnikov, giving 2-bromopropane.
- B.
With peroxide, HBr adds against Markovnikov's rule (the peroxide effect), giving 1-bromopropane.
- C.
HBr adds one H and one Br; 1,2-dibromopropane would come from adding Br2.
NCERT: Class 11 Chemistry, Chapter 9