CBSE Class 12-science Answered

(ii) Decreasing order of basic strength:

p- Toluidine > aniline > p- nitroaniline

This is because -NO₂ group has an electron withdrawing inductive effect or -I effect and -CH₃ group has electron releasing inductive effect or +I effect. Groups with -I effect decreases the electron density on the nitrogen of amino group and hence decreases the basic strength. Groups with +I effect increases the electron density on the nitrogen of amino group and hence increases the basic strength.

(iii) Increasing order of pKb value:

(C₂H₅)₂NH < C₂H₅NH₂ < C₆H₅NHCH₃ < C₆H₅NH₂

This is because -C6H5 group has an electron withdrawing inductive effect or -I effect and -C₂H₅ group has electron releasing inductive effect. Groups with -I effect decreases the electron density on the nitrogen of amino group and hence decreases the basic strength. Groups with +I effect increases the electron density on the nitrogen of amino group and hence increases the basic strength. Greater the basic strength the smaller is the pKb value.