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

Order of basic strength of aliphatic amine in aqueous solution is as follows (order of `K_b`)
`(CH_3)_2ddotNH gt CH_3ddotNH_2 gt (CH_3)_3 ddotN gt C_6H_5ddotNH_2`
As we know , `pK_b =-log K_b`
So, `(CH_3)_2 ddotNH` will have smallest `pK_b` value .
In case of phenyl amine, N is attached to `sp^2` -hybridised carbon, hence it has highest `pK_b` value and has least basic strength.