Which of the following is the corrent order of basicity in aqueous solution ? .

Options

A. `(C_(2)H_(5))_(3)Ngt(C_(2)H_(5))_(2)gt(C_(2)H_(5))_(2)NHgtC_(2)H_(5)NH_(2)gtNH_(3)`
B. `(C_(2)H_(5))_(2)NHgtC_(2)H_(5)NH_(2)gt(C_(2)H_(5))_(3)NgtNH_(3)`
C. `(C_(2)H_(5))_(2)NHgt(C_(2)H_(5))_(3)NgtC_(2)H_(5)NH_(2)gtNH_(3)`
D. `(C_(2)H_(5))_(3)NgtC_(2)H_(5)NH_(2)gt(C_(2)H_(5))_(2)NHgtNH_(3)`

Answer

C

Explanation

Two effects induction and solvation determine the `K_(b)` of an alky1 amine in aqueous solution Inductive effect dominates to make all three ethylamines stonger bases than `NH_(3)` and to make triethy1 amine stronger than ethylamine in aqueous solution the amine ions formed from `(C_(2)H_(5))_(2)NH` and `(C_(2)H_(5))_(3)` N are stabilized by solvation through H-bonding The aminium ion `Et_(3)`overset(+)NH formed from `(C_(2)H_(5))` N has only one hydrogen to use in hydrogen bonding to water molecules whereas the aminium ion `Et_(2)overset(+)NH_(2)` has two hydrogen Poorer solvation of the aminium ion formed from `(C_(2)H_(5))` N more than counteracts the electron releasing effect of the three ehty1 groups and makes the `(C_(2)H_(5))_(3)N` less basic than `(C_(2)H_(5))NH` in aqueous solution Free from solvation effects only inductive effect prevails and the order in gas phase is
`(C_(2)H_(5))_(3)Ngt(C_(2)H_(5))_(2)NHgtC_(2)H_(5)NH_(2)gtNH_(3)` .