Basic strength depends on

*Basic strength depends on:-

                                                  -> Inductive effect

                                                  -> Steric hindrance

                                                  -> Hydration energy

So, Dimethylamine is more basic than Trimethylamine in aqueous solution.

Reason:-

a. Less steric hindrance of Dimethylamine than Trimethylamine.

b. More hydration energy of Dimethylamine than Trimethylamine.

Example:-
a. CH₃-NH₂             b. (CH₃)₂-NH             c. (CH₃)₃-N

                                                                 -> More +I Effect

                                                                 -> More electron density

                                                                 -> More tendency to donate lone pair

                                                                     but H⁺ less acceptable lone pair

                                                                     due to Steric hindrance.

Order of basic strength:

(CH₃)₂-NH           >           (CH₃)-NH₂            >        (CH₃)₃-N

{Secondary amine}       {Primary amine}            {Tertiary amine}