Question

If amines are arranged in increasing order of their basic strength in gaseous phase, the correct order will be:

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

Hint:

In gaseous phase, basicity increases with number of alkyl groups due to inductive effect. In aqueous phase, solvation and steric hindrance alter this order.

Answer 1

The Correct Option is A

Basicity in gaseous phase is determined by electron-donating ability of alkyl groups which increase electron density on nitrogen. The more alkyl groups attached, the higher the basicity: - NH\(_3\): No alkyl group - CH\(_3\)NH\(_2\): One methyl group - (CH\(_3\))\(_2\)NH: Two methyl groups - (CH\(_3\))\(_3\)N: Three methyl groups Hence, basicity order increases as: \[ \boxed{\text{NH}_3<\text{CH}_3\text{NH}_2<(\text{CH}_3)_2\text{NH}<(\text{CH}_3)_3\text{N}} \] Note: This is valid for gaseous phase. In aqueous phase, steric hindrance and solvation affect order.