Explanation:

Friedel-Crafts alkylation is a type of electrophilic aromatic substitution reaction. When benzene undergoes Friedel-Crafts alkylation with 1-chloropropane, isopropyl benzene is obtained instead of n-propyl benzene. This is due to the nature of the reaction mechanism.

Mechanism of Friedel-Crafts Alkylation:

1. Formation of a Complex:

The reaction begins with the formation of a complex between the Lewis acid catalyst (AlCl3) and the electrophile (1-chloropropane). This complex is highly reactive and is capable of attacking the electron-rich benzene ring.

2. Formation of a Carbocation:

The complex attacks the benzene ring and forms a carbocation intermediate. This intermediate is highly unstable and can undergo rearrangement.

3. Rearrangement:

In the case of n-propyl chloride, the carbocation intermediate undergoes a hydride shift to form a more stable secondary carbocation. This carbocation then reacts with benzene to form n-propyl benzene.

However, in the case of isopropyl chloride, the carbocation intermediate can undergo a methyl shift to form a more stable tertiary carbocation. This carbocation then reacts with benzene to form isopropyl benzene.

4. Deprotonation:

The final step involves the removal of a proton from the newly formed alkylated benzene ring, which results in the formation of the final product.

Conclusion:

In summary, the formation of isopropyl benzene instead of n-propyl benzene in the Friedel-Crafts alkylation reaction between benzene and 1-chloropropane is due to the ability of the carbocation intermediate to undergo a methyl shift to form a more stable tertiary carbocation. This reaction mechanism highlights the importance of understanding the reactivity and stability of carbocation intermediates in electrophilic aromatic substitution reactions.