Question

Arrange the following in the decreasing 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 D iii > ii > i

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. 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. Thus the order of basic strength is $i<ii<iii$