Rearrange the following in an increasing order of their basic strengths:

C₆H₅NH₂, C₆H₅N(CH₃)₂, (C₂H₅)₂NH and CH₃NH₂.

Basicity of a compound is determined by its tendency to donate more electrons. If a compound is more electron rich, its tendency to donate electrons would be more so its basic strength would be more.

If groups showing electron pushing tendency (alkyl groups), are attached to the N atom, electron concentration would be more. Similarly more is the number of such groups, more is the basic strength.

So, 3° amines > 2° amines > 1° amine.

In, amines of benzene, the lone pair of nitrogen is not available for donation as they are delocalised over the benzene ring. So, their basic strengths are less than the alkyl amines.

Thus basic strength order is:-

C₆H₅NH₂ < C₆H₅N(CH₃)₂ < CH₃NH₂ < (C₂H₅)₂NH.