Question

What can be A and B in the following reaction?

• A. HBr, al
• B. KOH
• C. HBr, Peroxide alc. KOH
• D. HBr, Peroxide aq. KOH, $\Delta$

Hint:

Use peroxide for anti-Markovnikov addition of HBr. Alcoholic KOH always indicates elimination reactions.

Answer 1

The Correct Option is C

Step 1: Understanding the reaction components.
In hydrohalogenation of alkenes or alkynes, the reagent HBr can add via Markovnikov or anti-Markovnikov rule depending on the presence of peroxide. Step 2: Peroxide effect (Kharasch effect).
When HBr is used in the presence of peroxide, the reaction proceeds via a free radical mechanism and follows the anti-Markovnikov rule. Step 3: Role of alcoholic KOH.
Alcoholic KOH promotes elimination (E2) reactions to form alkenes. Step 4: Combining the steps.
First, HBr with peroxide adds to the alkene via anti-Markovnikov addition forming bromoalkane.
Then, alcoholic KOH eliminates HBr forming a new alkene. Hence, A = HBr with Peroxide and B = alcoholic KOH.