Considering the basec strength of amines in aqueous solution which one has the smallest `pK_b` value?

Options

A. `(CH_3)_2NH`
B. `CH_3NH_2`
C. `(CH_3)_3N`
D. `C_6H_5NH_2`

Answer

A

Explanation

It is known that `pK_b=logkk_b`
Thus, larger the value of `k_b`, smaller is the value of `pK_b` and hence stronger is the base. The order of basec strength of amines is as follows
`(CH_3)_2overset(..)NHgtCH_3overset(..)(N)H_2(CH_3)_3overset(..)(N)gtC_6H_5overset(..)(N)H_2`
The basic strength of amines depends on the inductive effect as well as steric hindrance of alkyl groups. Hence `(CH_2)_2`
`overset(..)(N)H` [secondary amine] possess the smallest value of `pK_b`