8.

Arrange the following in increasing order of their basic strength:

 

(i) C₆H₅ – NH₂, C₆H₅ – CH₂ – NH₂, C₆H₅ – NH – CH₃

 

(i) C₆H₅-NH₂ < C₆H₅-NH-CH₃ < C₆H₅-CH₂-NH₂
Reason:
C₆H₅-NH₂ will be least basic because of the delocalization of the lone pair of electrons present on the N-atom over the benzene ring due to the ‒R effect of the C₆H₅ group. However, C₆H₅-CH₂-NH₂ will be more basic than C₆H₅-NH-CH₃ because of the electron-releasing nature of the CH₃- a group that increases the electron density on the N-atom, making the lone pair of electrons on the N-atom easily available for donation to a proton. The basicity of C₆H₅-NH-CH₃ will be intermediate of C₆H₅-NH₂ and C₆H₅-CH₂-NH₂ because the C₆H₅- the group will tend to pull the electron density from the N-atom. On the other hand, the CH₃- group will tend to increase the electron density on the N-atom. Thus, the basic strength of the given amines will follow the above-mentioned order.

(ii) 

Reason:

The -CH₃ group will increase the electron density on the benzene ring because of it is +I effect, while the NO₂ group will decrease the electron density on the benzene ring because of its ‒I effect. Hence, the C₆H₅-NH₂ molecule having - the CH₃ group will be more basic than C₆H₅-NH₂. Also, it will be more basic than the C₆H₅-NH₂ molecule with the NO₂ group.