Question

What is the decreasing order of basicity of 1$^{\circ}$, 2$^{\circ}$ and 3$^{\circ}$ ethyl amines and ammonia?

• A. $NH_3 > C_2 H_5 NH_2 > (C_2 H_5)_2 NH > (C_2 H_5)_3 N$
• B. $(C_2 H_5)_3 N > (C_2 H_5)_2 NH > C_2 H_5 NH_2 > NH_3$
• C. $(C_2 H_5)_2 NH > C_2 H_5 NH_2 > (C_2 H_5)_3 N > NH_3$
• D. $(C_2 H_5)_2 NH > (C_2 H_5)_3 N > C_2 H_5 NH_2 > NH_3$

Answer 1

The Correct Option is D

The basicity of amines depends on their ability to donate an electron pair to a proton. The basicity of amines varies with their structure (primary, secondary, or tertiary) due to inductive effects and steric hindrance.

1. Primary amine (C_2H_5NH_2): These are basic due to the availability of a lone pair on the nitrogen atom, but the ethyl group provides a small electron-donating inductive effect.
2. Secondary amine ((C_2H_5)_2NH): Has two ethyl groups providing a greater inductive effect than primary amines, enhancing basicity further. Moreover, there is less steric hindrance compared to tertiary amines.
3. Tertiary amine ((C_2H_5)_3N): Although it has even more electron-donating groups, steric hindrance is high, which reduces the availability of its lone pair for protonation.
4. Ammonia (NH_3): Lacks any alkyl group but remains basic due to its lone pair, albeit less than any substituted amine.

Thus, the decreasing order of basicity in these compounds is:

1. Secondary Ethylamine (C_2H_5)_2NH
2. Tertiary Ethylamine (C_2H_5)_3N
3. Primary Ethylamine C_2H_5NH_2
4. Ammonia NH_3

The correct answer is: (C_2H_5)_2NH > (C_2H_5)_3N > C_2H_5NH_2 > NH_3

The option representing the above order according to the question is:

(C_2H_5)_2NH > (C_2H_5)_3N > C_2H_5NH_2 > NH_3