Amines

Amines

Question

Arrange the following in the increasing order of their pKb values:
C6H5NH2, C2H5NH2, C6H5NHCH3

Answer

pKb tells the strength of a base. Lower is pKb value, stronger is the base. Now C6H5NH2 is a weak base because the lone pair is involved in resonance with the benzene and is thus not available for a donation while in C2H5NH2, C2H5 is an electron donating group, which increases the e- density on N thus felicitating the release of lone pair. Hence, C2H5NH2 is a strong base.
Thus, the correct order is:

C2H5NH2< C6H5NHCH3< C6H5NH2

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