Question

What is the major product formed when Propene reacts with \(HBr\) in the presence of peroxide?

• A. \(2\)-Bromopropane
• B. \(1\)-Bromopropane
• C. \(1,2\)-Dibromopropane
• D. Propane

Hint:

Remember: \(HBr\) in the presence of peroxide follows the Anti-Markovnikov rule (Peroxide Effect). This effect is observed only with \(HBr\), not with \(HCl\) or \(HI\).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the outcome of an addition reaction between an asymmetric alkene (propene) and hydrogen bromide under specific radical-forming conditions (peroxide).
Step 2: Key Formula or Approach:
Normally, addition follows Markovnikov's rule. However, in the presence of organic peroxides, \( HBr \) adds via a free-radical mechanism.
This is known as the Anti-Markovnikov addition or the Kharasch effect.
Step 3: Detailed Explanation:
Propene structure: \( CH_3-CH=CH_2 \).
In the peroxide-induced mechanism, the bromine radical attacks the terminal carbon to form a more stable secondary carbon radical.
1. Initiation: Peroxide decomposes to form radicals.
2. Propagation: \( Br^\bullet \) adds to the terminal carbon of propene.
\[ CH_3-CH=CH_2 + Br^\bullet \to CH_3-\dot{C}H-CH_2Br \]
3. The resulting secondary radical then abstracts a hydrogen from another \( HBr \) molecule.
\[ CH_3-\dot{C}H-CH_2Br + HBr \to CH_3-CH_2-CH_2Br + Br^\bullet \]
The final product is \( 1 \)-bromopropane.
Step 4: Final Answer:
The major product is \( 1 \)-bromopropane.