Question

Arrange the following in increasing order of their basic strength :

C₆H₅ – NH₂, C₆H₅ – CH₂ – NH₂, C₆H₅ – NH – CH₃

Answer 1

C₆H₅-NH₂ < C₆H₅-NH-CH₃ < C₆H₅-CH₂-NH₂

Reason:-

C₆H₅-NH₂ will be least basic because of the delocalisation 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- 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- 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.