Read the following passage and answer questions.

Greater is the stability of the substituted ammonium cation, stronger should be the corresponding amine as a base. Thus, the order of basicity of aliphatic amines should be: primary > secondary > tertiary, which is opposite to the inductive effect based order. Secondly, when the alkyl group is small, like $-CH_3$ group, there is no staric hinderance to H-bonding. In case the alkyl group is bigger than $-CH_3$ group, there will be steric hinderance to H-bonding. Therefore, the change of nature of the alkyl group, e.g., from $-CH_3$ to $-C_2H_5$ results in change of the order of basic strength. Thus, there is a subtle interplay of the inductive effect, solvation effect and steric hinderance of the alkyl group which decides the basic strength of alkyl amines in the aqueous medium.

Which among the following amines is most basic in aqueous medium?

$(C_2H_5)_2NH$

The correct answer is Option (1) → $(C_2H_5)_2NH$
The basic strength of amines in aqueous medium depends on three factors:

1. +I (Inductive) effect of alkyl groups – Alkyl groups donate electron density to nitrogen, increasing basicity.

2. Solvation (Hydrogen bonding) of the ammonium ion – Better solvation stabilizes the conjugate acid, increasing basicity.

3. Steric hindrance – Bulky groups reduce solvation of the ammonium ion.

   So, The basic strength of amines in aqueous medium

   Secondary amines > Primary amines > Tertiary amines > NH₃

• NH₃ (Ammonia): No alkyl groups → weakest +I effect → lower basicity.

• C₂H₅NH₂ (Primary amine): One ethyl group gives +I effect → more basic than NH₃.

• (C₂H₅)₂NH (Secondary amine): Two ethyl groups provide stronger +I effect while still allowing good solvation → highest basicity in aqueous medium.

• (C₂H₅)₃N (Tertiary amine): Although it has strong +I effect, steric hindrance reduces solvation of the ammonium ion, lowering its basicity in water.

Thus the order is:

(C₂H₅)₂NH > C₂H₅NH₂ > (C₂H₅)₃N > NH₃

Secondary amines > Primary amines > Tertiary amines > NH₃

Therefore, the most basic amine in aqueous medium is (C₂H₅)₂NH.