Read the passage carefully and answer the questions.
Amines are considered as derivatives of ammonia obtained by replacement of hydrogen atoms with alkyl or aryl groups. In nature they occur among proteins, vitamins, alkaloids and hormones. These can be primary, secondary or tertiary depending on the number of hydrogen groups replaced. They can be prepared from nitro compounds, alkyl halides, nitriles, amides etc. Due to unshared pair of electrons they behave as Lewis bases. Influence of the number of hydrogen atoms at nitrogen atom is displayed in physical properties such as solubility, boiling point and chemical reactions including basicity. Basic character of amines is expressed in terms of their \( K_b \) and \( pK_b \) values. Three classes of amines can be distinguished with p-toluene sulphonyl chloride which reacts with primary and secondary amines. Amino group when attached to benzene ring behaves as an activating and ortho para directing group.
Which of the following reaction is not given by aniline?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Friedel-Crafts Reaction
The –\( \ce{NH2} \) group of aniline is a Lewis base and a powerful activating, ortho/para-directing group. Aniline therefore reacts readily at nitrogen (alkylation, acylation) and on the ring (bromination). The Friedel-Crafts reaction needs anhydrous \( \ce{AlCl3} \), a Lewis acid, which forms a salt with aniline instead:
\( \displaystyle \ce{C6H5NH2 + AlCl3 -> C6H5NH2-AlCl3}\ (\text{salt}) \)
Option (1) Alkylation — Given by aniline (N-alkylation). Aniline is a nucleophile and reacts with an alkyl halide at the nitrogen atom, giving a secondary amine (and further alkylated products):
\( \displaystyle \ce{C6H5NH2 + CH3Cl -> C6H5NHCH3 + HCl} \)
Option (2) Acylation — Given by aniline (N-acylation). Aniline reacts with acid chlorides or anhydrides by nucleophilic substitution at nitrogen; a base such as pyridine removes the HCl formed:
\( \displaystyle \ce{C6H5NH2 + CH3COCl} \xrightarrow{\text{pyridine}} \ce{C6H5NHCOCH3 + HCl} \)
Option (3) Bromination — Given by aniline. The ring is so activated that bromine water at room temperature gives a white precipitate of 2,4,6-tribromoaniline:
\( \displaystyle \ce{C6H5NH2 + 3Br2} \xrightarrow{\ce{H2O}} 2,4,6\text{-}\ce{Br3C6H2NH2 v + 3HBr} \)
Option (4) Friedel-Crafts Reaction — Not given by aniline. In the salt the nitrogen carries a positive charge and becomes a strongly deactivating group, so the ring does not undergo Friedel-Crafts alkylation or acylation.
NCERT (2026-27 edition):
Electrophilic Substitution – …
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| 22-05 S2 | 13-05 S2 | – | – | – |