Arrange the following in increasing order of their basic strength :
` C_2 H_5 NH_2 . C_6 H_5 NH_2 ,CH_2 and (C_2 H_5) NH `

Explanation

Due to the +I effect of `C_2 H_5` group, `(C_2 H_3)_2NH` (having two `C_2 H_5` groups attached to N) is more basic than `C_2 H_5 NH_2`. Now aromatic amines, i.e., `C_6 H_5 NH_2` and `C_6 H_5 CH_2 NH_2` are less basic than `C_2 H_5 NH_2` due to -I effect of `C_6 H_5 ` group. Out of `C_6 H_5 NH_2` and `C_6 H_5 CH_2 NH_2, C_6 H_5 NH_2` in which `C_6 H_5` group is directly linked to `NH_2` group is less basic than `C_6 H_5 CH_2 NH_2`. This is because the lone pair of electrons on nitrogen atoms is delocalized over the benzene ring resulting in decrease in electron density on nitrogen. Therefore, the lone pair of electrons on N atom in `C_6 H_5 CH_2 NH_2` is more easily available for protonation than that on the N-atom in `C_6 H_5 NH_2`. Hence, `C_6 H_5 CH_2 NH_2 ` is more basic than `C_6 H_5 NH_2`. Therefore, the correct order of the basic character is : `C_6 H_5 NH_2 lt C_6 CH_2 NH_2 lt C_2 H_5 NH_2 lt (C_2 H_5) NH `