Question

The major product(P) in the following reaction is

• A.

  

• B.

  

• C.

  

• D.

  

Answer 1

The Correct Option is D

To determine the major product \( P \) in the given reaction, let's analyze the reaction step-by-step:

1. Reactants and Conditions: The reactant is an allylic ether with an alkene group. The reagent used is concentrated HBr in excess under heated conditions. 
2. Mechanism of Reaction:
   • Initially, HBr will protonate the ether oxygen, leading to the formation of an oxonium ion. This makes the ether cleavage favorable, resulting in the formation of a primary carbocation after the elimination of an alcohol group.
   • The excess HBr under heated conditions is likely to add across the double bond of the alkene in a Markovnikov fashion (where the bromine adds to the more substituted carbon), leading to a haloalkane.
   • If any rearrangement is possible, it will lead to a more stable carbocation intermediate, which is likely here due to resonance stabilization between the formed carbocation and the aromatic ring.
   • Ultimately, this will result in substitution or addition reactions that stabilize the intermediate carbocation by forming a more stable product.
3. Conclusion: Given the reaction conditions and the nature of reagents, the major product will involve the cleavage of the ether and the Markovnikov addition of HBr across the double bond.

Based on these steps, option D represents the structure that matches the expected major product of this reaction.

Answer 2

In this reaction, an alkene side chain attached to the benzene ring reacts with excess con centrated HBr.
The mechanism involves the following steps:
Step 1. The double bond in the alkene reacts with HBr to form a carbocation intermediate.
Step 2. Due to excess HBr, the benzyl carbo cation rearranges to a more stable form.
Step 3. The addition of Br takes place, resulting in the formation of the major product, which is the bromo-substituted alkane on the benzene ring.
Thus, the major product is: