Identify A.

The correct answer is Option (2) → C₆H₅C(CH₃)=NCH₃ (N-methyl imine, a Schiff’s base)

Ammonia and its derivatives H₂N–Z add to the carbonyl group of aldehydes and ketones. The reaction is reversible and acid catalysed: the nitrogen of the amine attacks the carbonyl carbon (nucleophilic addition), and the addition product quickly loses water to form a C=N bond. With a primary amine (Z = R) the product is a substituted imine, or Schiff’s base.

Here acetophenone reacts with methylamine:

    \( \ce{C6H5COCH3 + H2NCH3} \xrightarrow{\ce{H^+}} \ce{C6H5C(CH3)=NCH3 + H2O} \)

So A is the N-methyl imine of acetophenone, the structure in Option (2).

Why the other options are incorrect

• Option (1) 2-(methylamino)acetophenone — Incorrect. The amine reacts with the C=O group, not with the ring; the carbonyl group is still present in this structure, so no reaction has taken place at it.

• Option (3) 3-(methylamino)acetophenone — Incorrect. Again an –\( \ce{NHCH3} \) group on the ring with the C=O group untouched; amines do not substitute a hydrogen of the benzene ring.

• Option (4) N-methyl-1-phenylethanamine, C₆H₅CH(CH₃)NHCH₃ — Incorrect. This amine forms only if the imine is reduced further (for example with \( \ce{H2} \)/Ni); there is no reducing agent here.

NCERT (2026-27 edition):
Addition of Ammonia and its Derivatives – …