The product obtained as a result of reaction of benzene with n-propyl chloride in presence of $AlCl_{3}$:

Question

Accepted Answer

The reaction of benzene with n-propyl chloride in the presence of aluminum chloride ($AlCl_{3}$) is an example of a Friedel-Crafts alkylation reaction. In this reaction, the role of $AlCl_{3}$ is to act as a Lewis acid catalyst, which facilitates the formation of a carbocation from the alkyl chloride.

1. **Explanation for Option 2 (iso-propyl benzene):**
   - When n-propyl chloride is treated with $AlCl_{3}$, it forms a primary carbocation. However, primary carbocations are not very stable. Therefore, a rearrangement occurs to form a more stable secondary carbocation. In this case, the primary n-propyl carbocation rearranges to form a secondary isopropyl carbocation.
   - The isopropyl carbocation is more stable due to hyperconjugation and inductive effects, which stabilize the positive charge.
   - This stable isopropyl carbocation then reacts with benzene to form iso-propyl benzene (cumene) as the major product.

2. **Explanation for why other options are incorrect:**
   - **Option 1 (propenyl benzene):** This option suggests the formation of an alkene (propenyl group) attached to benzene. However, the Friedel-Crafts alkylation mechanism involves the formation of a carbocation, not an alkene. Therefore, propenyl benzene is not formed in this reaction.
   - **Option 3 (n-propyl benzene):** Although n-propyl chloride is the starting material, the primary n-propyl carbocation is not stable and undergoes rearrangement to form the more stable isopropyl carbocation. As a result, n-propyl benzene is not the product of this reaction.
   - **Option 4 (ethyl benzene):** Ethyl benzene would require an ethyl group to be attached to benzene. Since the starting material is n-propyl chloride, not ethyl chloride, ethyl benzene cannot be the product of this reaction.

In conclusion, the correct product of the reaction between benzene and n-propyl chloride in the presence of $AlCl_{3}$ is iso-propyl benzene, making Option 2 the correct answer.