Chemistry · Amines · NEET
In aniline the nitrogen lone pair is free. After acylation the nitrogen sits next to a carbonyl (C=O). The lone pair now moves toward the oxygen atom by resonance, forming a partial N=C and putting negative charge on oxygen. Because this lone pair is tied up with the electron-hungry carbonyl, it is much less available to grab a proton or to donate into the ring. Less available lone pair means lower reactivity.
Weaker. Basicity depends on how freely the nitrogen lone pair can accept a proton. In acetanilide the lone pair is delocalised onto the carbonyl oxygen, so it is less available for protonation. That is why the -NHCOCH3 group is a weaker base than the -NH2 group of aniline.
Aniline is very reactive to electrophiles because the free lone pair pushes electron density into the ring at ortho and para positions. In acetanilide part of that lone pair is pulled toward the amide oxygen instead of the ring, so less electron density reaches the ring. NCERT states directly: the activating effect of -NHCOCH3 is less than that of -NH2. It still activates, but more gently and in a controlled way.
Free aniline is so reactive that reactions become hard to control (it can over-substitute and give tar-like oxidation products in strong acid). By acetylating it to acetanilide first, we lower the reactivity to a manageable level, do the substitution mainly at the para position, then hydrolyse the amide back to the free amine. Acetylation is a temporary protecting step for the -NH2 group.
Yes. Acid (or base) hydrolysis of the amide converts acetanilide back to aniline: C6H5NHCOCH3 with HCl/H2O and heat gives C6H5NH2. This reversibility is exactly why acetylation works as a protecting group — you deactivate, react, then remove the acyl group to recover the amine. A ReNEET 2026 PYQ tests this hydrolysis directly.
Identify the reactions which give aniline as the major product. (A) C6H5CN with LiAlH4; (B) C6H5CONH2 with KOH, Br2; (C) C6H5NO2 with NaBH4; (D) C6H5NHCOCH3 with HCl, H2O, heat. Choose the correct answer:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Acetanilide is the acylated form of aniline, C6H5NHCOCH3. It is made by reacting aniline with acetic anhydride (or acetyl chloride). The N-H of aniline is replaced by N-COCH3, so the nitrogen now carries an acetyl (acyl) group.
Yes, but weakly. -NHCOCH3 is still an ortho/para-directing activating group, just a milder one than -NH2. NCERT says the activating effect of -NHCOCH3 is less than that of the amino group, because part of the lone pair is shared with the carbonyl oxygen.
In any amide, the nitrogen lone pair is delocalised into the adjacent C=O group (resonance gives a partial N=C double bond and negative charge on oxygen). This same delocalisation makes amides very weak bases and makes acetanilide less reactive than a normal amine.
Aniline is very reactive and easily oxidised in strong acid, giving tarry by-products; also in acid it becomes the anilinium ion (-NH3+), which is meta-directing, so you get a mixture. Acetylating first to acetanilide avoids these problems and gives clean para-substitution.
Yes. The protection is temporary: after the desired substitution, hydrolysis of the amide bond (acid or base with heat) regenerates the free amine. Knowing acetanilide gives aniline back on hydrolysis is a commonly tested point.
