Aniline does not undergo Friedel-Crafts reaction because

(A) It forms salt with Lewis acid catalyst, \(AlCl_3\)

(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.

Choose the correct answer from the options given below:

A, C and D only

The correct answer is option 3. A, C and D only.

Aniline (C6H5NH2) does not undergo Friedel-Crafts reactions effectively, and the correct explanation involves the behavior of aniline in the presence of a Lewis acid catalyst like \( AlCl_3 \). Let us analyze each option:

(A) It forms salt with Lewis acid catalyst, \( AlCl_3 \)

Aniline contains a lone pair of electrons on the nitrogen atom. When reacted with a Lewis acid catalyst like \( AlCl_3 \), the lone pair on nitrogen can coordinate with the Lewis acid to form a complex or salt. This complex formation reduces the availability of the lone pair of electrons on nitrogen for participating in the reaction mechanism required for the Friedel-Crafts reaction.

The complexation with \( AlCl_3 \) decreases the nucleophilic nature of nitrogen, hindering its ability to participate in the reaction.

(B) Nitrogen of aniline acquires negative charge

This statement is incorrect. When aniline reacts with a Lewis acid catalyst, the lone pair of electrons on the nitrogen atom is utilized in forming a coordination complex with the Lewis acid, which reduces the nucleophilicity of nitrogen. However, nitrogen itself does not acquire a negative charge.

[AdditionalInformation: The \(AlCl_3\) catalyst intended to function as a Lewis acid in Friedal-Crafts reactions, functions as a Lewis base in the presence of aniline and forms an insoluble salt. The reason for this behaviour is that \(AlCl_3\) is electron deficient and reacts with the lone pair of the aniline amine group. This prevents the reaction from occurring.]

(C) Nitrogen of aniline acquires positive charge

When aniline reacts with a Lewis acid catalyst like \( AlCl_3 \), the lone pair of electrons on the nitrogen atom is donated to the Lewis acid, leading to the formation of a coordinate covalent bond. This donation of electrons results in the nitrogen atom acquiring a partial positive charge, making it less available to stabilize the intermediates formed during the Friedel-Crafts reaction.

The positive charge on nitrogen further deactivates the aromatic ring toward electrophilic attack, impeding the Friedel-Crafts reaction.

(D) Nitrogen acts as a strong deactivating group in the further reaction

While nitrogen itself is not a strong deactivating group, the complexation with the Lewis acid catalyst affects the availability of nitrogen to stabilize intermediates formed during the Friedel-Crafts reaction. This reduced availability deactivates the aromatic ring toward further electrophilic attack, hindering subsequent reactions.

The complexation with the Lewis acid effectively deactivates the ring, preventing efficient participation in further reactions.

In summary, aniline does not effectively undergo the Friedel-Crafts reaction due to its interaction with the Lewis acid catalyst, \( AlCl_3 \), which leads to the formation of a coordination complex, reduces the nucleophilicity of nitrogen, induces a partial positive charge on nitrogen, and deactivates the aromatic ring toward further electrophilic attack. Therefore, the correct combination of reasons explaining why aniline does not undergo the Friedel-Crafts reaction is: 3. A, C and D only