Question

$3$-Methylpent-$2$-ene on reaction with $HBr$ in presence of peroxide forms an addition product. The number of possible stereoisomers for the product is :

• A. Two
• B. Four
• C. Six
• D. Zero

Answer 1

The Correct Option is B

To determine the number of stereo isomers formed when 3-Methylpent-2-ene reacts with HBr in the presence of peroxide, we need to understand the mechanism involved. This reaction follows the anti-Markovnikov rule due to the presence of peroxides, which leads to the formation of free radicals.

1. Reaction Mechanism:
   1. The presence of peroxides leads to the formation of free radicals.
   2. The alkene, 3-Methylpent-2-ene, will react with the HBr radical, adding the bromine to the less substituted carbon due to the anti-Markovnikov rule.
   3. This will produce 3-bromo-3-methylpentane.
2. Chirality:
   • The carbon atom to which the bromine atom is attached in the product (3-bromo-3-methylpentane) becomes a chiral center.
   • The molecule has two chiral centers resulting in stereochemistry:
     • The first chiral center is the carbon to which Bromine attaches.
     • The second chiral center is inherent from the structure of the molecule, due to the presence of different groups attached to the carbon atom.
3. Calculating Stereoisomers:
   • Each chiral center contributes to stereo isomerism.
   • The formula for calculating the number of stereoisomers is \(2^n\), where \(n\) is the number of chiral centers.
   • Here, \(n = 2\), hence the number of stereoisomers is \(2^2 = 4\).
4. Conclusion: Thus, the correct answer is Four.