The correct decreasing order of basic strength of following amines in aqueous medium is.
(A) $(C_2H_5)_3N$
(B) $(C_2H_5)_2NH$
(C) $C_2H_5NH_2$
(D) $NH_3$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B), (A), (C), (D)
The decreasing order of basic strength of the given amines in aqueous medium is:
(C₂H₅)₂NH > (C₂H₅)₃N > C₂H₅NH₂ > NH₃
In aqueous medium, basic strength depends on:
-
+I (electron-donating) effect of alkyl groups
-
Solvation of the conjugate acid (RNH₃⁺, R₂NH₂⁺, R₃NH⁺)
1. Secondary amine → (C₂H₅)₂NH
-
Strong +I effect (two ethyl groups)
-
Good solvation of protonated form
Most basic
2. Tertiary amine → (C₂H₅)₃N
-
Strong +I effect (three ethyl groups)
-
But poor solvation due to steric hindrance
Less basic than secondary
3. Primary amine → C₂H₅NH₂
-
Moderate +I effect
-
Good solvation
Less basic than 2° and 3°
4. NH₃
-
No +I effect
Least basic
So the correct answer is (B), (A), (C), (D)
(C₂H₅)₂NH > (C₂H₅)₃N > C₂H₅NH₂ > NH₃