Question

Which from following is a correct increasing order of basic strength of compounds?

• A. \((\mathrm{CH}_{3})_{2}\mathrm{NH}<\mathrm{CH}_{3}\mathrm{NH}_{2}<(\mathrm{CH}_{3})_{3}\text{ }\mathrm{N}<\mathrm{NH}_{3}\)
• B. \(\mathrm{NH}_{3}<(\mathrm{CH}_{3})_{2}\mathrm{NH}<\mathrm{CH}_{3}\mathrm{NH}_{2}<(\mathrm{CH}_{3})_{3}\text{ }\mathrm{N}\)
• C. \(\mathrm{CH}_{3}\mathrm{NH}_{2}<(\mathrm{CH}_{3})_{2}\mathrm{NH}<(\mathrm{CH}_{3})_{3}\text{ }\mathrm{N}<\mathrm{NH}_{3}\)
• D. \(\mathrm{NH}_{3}<(\mathrm{CH}_{3})_{3}\text{ }\mathrm{N}<\mathrm{CH}_{3}\mathrm{NH}_{2}<(\mathrm{CH}_{3})_{2}\mathrm{NH}\)

Hint:

In aqueous solution, basic strength of methyl amines depends on both inductive effect and solvation of the ammonium ion.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
In water, the order of basic strength for methyl amines is \((\text{CH}_3)_2\text{NH}>\text{CH}_3\text{NH}_2>(\text{CH}_3)_3\text{N}>\text{NH}_3\).

Step 2: Reasoning
Methyl groups push electrons and increase basicity, but the tertiary amine is less stabilised by hydrogen bonding after protonation, so it falls below the primary amine.

Step 3: Write in increasing order
\(\text{NH}_3\lt(\text{CH}_3)_3\text{N}\lt\text{CH}_3\text{NH}_2\lt(\text{CH}_3)_2\text{NH}\), which is option (D).

Final Answer:
The correct increasing order is \(\text{NH}_3 \lt (\text{CH}_3)_3\text{N} \lt \text{CH}_3\text{NH}_2 \lt (\text{CH}_3)_2\text{NH}\). \[ \boxed{\text{(D) }\text{NH}_{3}\lt(\text{CH}_{3})_{3}\text{N}\lt\text{CH}_{3}\text{NH}_{2}\lt(\text{CH}_{3})_{2}\text{NH}} \]