Q. 4 B4.1( 7 Votes )

Arrange the following:

In increasing order of basic strength:

C6H5NH2, C6H5N(CH3)2, (C2H5)2NH and CH3NH2

Answer :

In (C2H5)2NH2, two ethyl groups are present and in CH3NH2 one methyl group is present. As we know that more alkyl groups are


present, more basic will be the amine. Hence, (C2H5)2NH2 is more basic than the CH3NH2


Now in C6H5NH2, due to delocalisation of lone pair of electrons of the N-atom over the benzene ring (decreases the electron density of N-atom) makes it less basic than (C2H5)2NH2 and CH3NH2


Now, in C6H5N(CH3)2 due to presence of two CH3 groups (increases the electron density of N-atom) makes it more basic than C6H5NH2 but less basic than (C2H5)2NH2 and CH3NH2 due to the presence of aromatic ring which is responsible for the delocalisation of lone pair of electrons of N-atom over the benzene ring (decreases the electron density of N-atom)


Combining all these facts, the relative basic strength of these four amines increases in the order:


C6H5NH2 < C6H5NHCH3 < CH3NH2 < (C2H5)2NH


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