CBSE Class 12-science Answered

(i) In aniline, the lone pair of electrons on the N atom is delocalised over the benzene ring. As a result, the electron density on the nitrogen atom decreases. In contrast, in CH₃NH₂, the +I effect of CH₃ increases the electron density on the N atom. Therefore, aniline is a weaker base than methylamine. Hence, its pKb value is higher than that of methylamine.

(ii) Being more basic than water, methylamine accepts a proton from water-liberating OH− ions.

These OH− ions combine with Fe³⁺ ions present in H₂O to form a brown precipitate of hydrated ferric oxide.

(iii) Being a Lewis base, aniline reacts with Lewis acid AlCl₃ to form a salt.

As N of aniline acquires +ve charge, it acts as a strong deactivating group for electrophilic substitution reaction. Consequently, aniline does not undergo Friedel-Crafts reaction.