Question

Aniline does not undergo Friedel-Crafts reaction because 1.(A) It forms salt with the Lewis acid catalyst, AlCl₃.
2. (B) Nitrogen of aniline acquires negative charge.
3. (C) Nitrogen of aniline acquires positive charge.
4. (D) Nitrogen acts as a strong deactivating group in the further reaction.

• (A) It forms salt with the Lewis acid catalyst, AlCl3
• (B) Nitrogen of aniline acquires negative charge
• (C) Nitrogen of aniline acquires positive charge
• (D) Nitrogen acts as a strong deactivating group in the further reaction

Answer 1

The Correct Option is C

Aniline does not undergo the Friedel-Crafts reaction due to the behavior of the nitrogen atom in the presence of a Lewis acid catalyst like AlCl₃. In such a reaction, an electrophile is formed typically by the interaction of an alkyl or acyl halide with a Lewis acid. However, in the case of aniline, the nitrogen atom disrupts this process. Here's why: 

1. Aniline contains an amino group (-NH₂), where nitrogen has a lone pair of electrons.

2. When aniline is exposed to a Lewis acid like AlCl₃, the nitrogen donates its lone pair of electrons to the Lewis acid due to its affinity to form a bond.

3. This donation leaves a positive charge on the nitrogen atom, thereby converting the amino group into an electron-deficient site.

4. As a result, the nitrogen acquires a positive charge, which destabilizes the aromatic ring, thus preventing the formation of the necessary carbocation intermediary required for the Friedel-Crafts alkylation or acylation reaction to proceed efficiently.

Therefore, the correct explanation is: (C) Nitrogen of aniline acquires positive charge.

Answer 2

Aniline does not undergo Friedel-Crafts reactions due to the interaction of its amino group with the Lewis acid catalyst, such as AlCl₃. Here is the explanation: 

1. Aniline has an amino group (-NH₂), where the nitrogen atom possesses a lone pair of electrons.

2. When aniline is exposed to a Lewis acid catalyst like AlCl₃, the lone pair of nitrogen interacts with the catalyst, forming a coordination bond.

3. This interaction leads to the formation of a complex in which the nitrogen atom, having donated its lone pair, acquires a positive charge.

4. The development of a positive charge on the nitrogen of the amino group results in a significant decrease in the electron density of the benzene ring, making the ring much less reactive towards electrophilic substitution reactions.

5. Hence, the formation of this positively charged nitrogen complex deactivates the aniline towards Friedel-Crafts reactions.

Therefore, the correct option is: (C) Nitrogen of aniline acquires positive charge.