Question

Choose the correct order of basicity of the following compounds :

• A. $\left(a\right)>\left(b\right)>\left(c\right)$
• B. $\left(c\right)>\left(b\right)>\left(a\right)$
• C. $\left(c\right)>\left(a\right)>\left(b\right)$
• D. $\left(b\right)>\left(a\right)>\left(c\right)$

Answer 1

The correct option is C $\left(c\right)>\left(a\right)>\left(b\right)$

In (b) :
Due to steric inhibition of protonation,the conjugate acid of ortho substituted aniline becomes destabilised due to steric hindrance . So (b) is the least basic compound.

Between (a) and (c):
In (a) there are 2 methyl groups attached to nitrogen that show +I effect and hence increase the electron density, making the lone pair available for donation.
In (c) :


due to steric hindrance $-N(C{H}_3{)}_2$ group goes out of plane, so resonance with the ring is hampered. Lone pair becomes more available to accept $H^{+}$ as comapred to (a) so basicity increases and due to steric inhibition of resonance (c) is the most basic compound.
Correct order is :
(c) > (a) > (b)