JEE Main 2025 Apr 2 Shift 1, Chemistry Q13: Properties of Amines

JEE Main2025Apr 2, Shift 1Chemistry

The correct order of basic nature on aqueous solution for the bases $N H_{3}$ , $H_{2} N - N H_{2}$ , $C H_{3} C H_{2} N H_{2}$ , $(C H_{3} C H_{2})_{2} N H$ and $(C H_{3} C H_{2})_{3} N$ is :

A
$N H_{3} < H_{2} N - N H_{2} < (C H_{3} C H_{2})_{3} N < C H_{3} C H_{2} N H_{2} < (C H_{3} C H_{2})_{2} N H$
B
$N H_{3} < H_{2} N - N H_{2} < C H_{3} C H_{2} N H_{2} < (C H_{3} C H_{2})_{2} N H < (C H_{3} C H_{2})_{3} N$
C
$H_{2} N - N H_{2} < N H_{3} < (C H_{3} C H_{2})_{3} N < C H_{3} C H_{2} N H_{2} < (C H_{3} C H_{2})_{2} N H$
D
$N H_{2} - N H_{2} < N H_{3} < C H_{3} C H_{2} N H_{2} < (C H_{3} C H_{2})_{3} N < (C H_{3} C H_{2})_{2} N H$

Solution

Basicity in aqueous solution reflects the balance of three effects on the conjugate ammonium ion: alkyl $+ I$ donation (raises basicity), solvation by hydrogen bonding (more N–H bonds give better stabilisation), and steric crowding (lowers accessibility).

The empirically observed order for ethyl amines in water is:

$(C_{2} H_{5})_{2} N H > (C_{2} H_{5})_{3} N > C_{2} H_{5} N H_{2} > N H_{3}$

Hydrazine is less basic than ammonia because the second – $N H_{2}$ group is electron-withdrawing through induction and destabilises the conjugate acid:

$H_{2} N - N H_{2} < N H_{3}$

Combining the two pieces:

$H_{2} N - N H_{2} < N H_{3} < C_{2} H_{5} N H_{2} < (C_{2} H_{5})_{3} N < (C_{2} H_{5})_{2} N H$

$∴$ Option (4) matches.

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JEE Main 2025 Apr 2 Shift 1, Chemistry Q13: Properties of Amines

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