As it is known that electron-releasing group increases the basic strength and electron withdrawing group decreases the basic strength of −NH2 group.
As in
group is planked between two electron withdrawing groups, compound (1) is least basic among all. In compound (2),−NH− is attached with one electron withdrawing group −CO− and one electron releasing group −CH3, it is a bit basic than compound
(1). In compound (4)- COCH 3, group is attached to aniline ring, not directly with −NH2 group.
Hence it is more basic than compound (2). Compound (3) is most basic among all compounds since in it, −NH2 is atached to only one electron releasing group (−CH2−). Thus, the correct order of basic strength will be
