In phenyl methanamine, the lone pair on nitrogen of
−NH2 group is localised and does not undergoes resonance as attached to
sp3-hybridised C-atom.
Phenyl methanamine or benzyl amine
(B),(C) and
(D) are aromatic amines in which lone pair of electrons of N-atoms goes in resonance
(+
R effect) with the benzene ring. So, Lewis basicity or donation of lone of electrons of these amines will be decreased in comparison to (A).
+I effects of two
−CH3 groups are in compensation with
−R effect of the ring.
+ l effect of one
−CH3 group is trying to compensate
−R effect of the ring.
It has no
+ leffect on
N-atom to outweigh
−R-effect of the ring.
So,
A is purely aliphatic
1∘-amine.
B is aromatic
3∘-amine with more aliphatic nature (for two
−CH3 groups).
C is aromatic
2∘-amine with less aliphatic nature (for one
−CH3 group).
D is purely aromatic
1∘-amine. Hence basicity order is
A>B>C>D.