Question

Assertion(A): Propene reacts with HBr in presence of organic peroxide gives 1-bromopropane.
Reason(R): The reaction occurs through carbocation intermediate.

• A. Both A and R are true but R is not the correct explanation.
• B. A is false but R is true.
• C. A is true but R is false.
• D. Both A and R are true and R is the correct explanation.

Hint:

Peroxide effect is observed only with HBr and not with HCl or HI because only HBr gives energetically favorable radical chain mechanism.

Answer 1

The Correct Option is C

Concept: Addition of HBr to alkenes normally follows Markovnikov rule. However, in presence of peroxide, the reaction follows anti-Markovnikov addition through free radical mechanism. This phenomenon is known as: \[ Kharasch Effect \]

Step 1: Verification of Assertion Propene: \[ \mathrm{CH_3CH=CH_2} \] in presence of: \[ \mathrm{HBr/peroxide} \] undergoes anti-Markovnikov addition. Therefore bromine attaches to terminal carbon. Thus product formed is: \[ \mathrm{CH_3CH_2CH_2Br} \] which is: \[ \mathrm{1\text{-}Bromopropane} \] Hence, Assertion is true.

Step 2: Verification of Reason The reason states that reaction proceeds through carbocation intermediate. This is incorrect. In presence of peroxide, the mechanism involves:
• Formation of free radicals
• Radical chain propagation
• Radical intermediate No carbocation intermediate is formed. Therefore, the Reason is false. Hence: \[ \boxed{\text{Assertion is true but Reason is false}} \] Thus, the correct answer is: \[ \boxed{(C)} \]