Question

Arrange the following in the increasing order of basic strength:
i) $C_6{H}_5{NH}_2$
ii) $C_6{H}_5{NHCH}_3$
iii) $C_6{H}_5{CH}_2{NH}_2$

• A. i < ii < iii
• B. ii < i < iii
• C. iii < i < ii
• D. iii < ii < i

Answer 1

The correct option is A i < ii < iii

In aniline ($C_6{H}_{5}N{H}_2$) lone pair of electrons is in conjugated system with benzene ring thus is less available. In Benzyl amine ($C_6{H}_5-C{H}_{2}N{H}_2$) the lone pair is not in conjugation and easily available to react with the activating effect of the benzyl group. Thus it is the strongest base. The $-C{H}_3$ group in $C_6{H}_{5}NHC{H}_3$ is an activating group which releases electrons to the ring and makes it a strong base but the electron lone pair is in conjugation with the ring and less available. The order of basic strength is $i<ii<iii$