Arrange the following in the decreasing order of basic strength in gas phase:
(A) \( C_2H_5NH_2 \)
(B) \( (C_2H_5)_2NH \)
(C) \( (C_2H_5)_3N \)
(D) \( NH_3 \)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (C), (B), (A), (D)
In the gas phase there is no solvent, so only the +I effect of the alkyl groups decides, and basicity rises with the number of alkyl groups:
\( \displaystyle \text{tertiary amine} \gt \text{secondary amine} \gt \text{primary amine} \gt \ce{NH3} \)
Matching the labels:
(C) \( \ce{(C2H5)3N} \): tertiary amine, three ethyl groups
(B) \( \ce{(C2H5)2NH} \): secondary amine, two ethyl groups
(A) \( \ce{C2H5NH2} \): primary amine, one ethyl group
(D) \( \ce{NH3} \): no alkyl group
Shortcut: In the gas phase the tertiary amine is the strongest and ammonia the weakest base, so the order starts with (C) and ends with (D): only Option (4).
NCERT (2026-27 edition):
Alkanamines versus Ammonia – …
