Question

Identify strongest base from following in aqueous medium.

• A. \(\text{NH}_3\)
• B. \(\text{CH}_3\text{NH}_2\)
• C. \((\text{CH}_3)_2\text{NH}\)
• D. \((\text{CH}_3)_3\text{N}\)

Hint:

For lower aliphatic amines in aqueous medium: \[ 2^\circ > 1^\circ > 3^\circ > \text{NH}_3 \]

Answer 1

The Correct Option is C

Concept:
In aqueous medium, the basic strength of aliphatic amines depends on:
• electron releasing effect of alkyl groups
• solvation of the protonated amine Because of the balance between these two effects, the order in aqueous medium is commonly: \[ 2^\circ > 1^\circ > 3^\circ > \text{NH}_3 \]

Step 1: Compare the given bases.

• \(\text{NH}_3\) has no alkyl group.
• \(\text{CH}_3\text{NH}_2\) is primary amine.
• \((\text{CH}_3)_2\text{NH}\) is secondary amine.
• \((\text{CH}_3)_3\text{N}\) is tertiary amine.

Step 2: Use the order in aqueous medium.
In water, secondary amine is strongest because it gets good +I effect and still gets sufficient solvation. So the strongest base is: \[ (\text{CH}_3)_2\text{NH} \] Hence, the correct answer is:
\[ \boxed{(C)\ (\text{CH}_3)_2\text{NH}} \]