Question

In case of substituted aniline the group which decreases the basic strength is

• A. $-NH_2$
• B. $-OCH_3$
• C. $-NO_2$
• D. $-CH_3$

Hint:

Electron-withdrawing groups reduce the basicity of aniline by pulling electron density away from the nitrogen atom.

Answer 1

The Correct Option is C

Step 1: Understand basic strength of aniline.
The basic strength of aniline depends on the availability of the lone pair of electrons on the nitrogen atom for protonation. Electron-donating groups increase basicity, while electron-withdrawing groups decrease it.
Step 2: Analyze the effect of substituents.
(A) $-NH_2$: It is an electron-donating group (+M effect), which increases basic strength.
(B) $-OCH_3$: It also shows +M effect and increases basicity.
(C) $-NO_2$: It is a strong electron-withdrawing group due to both $-I$ and $-M$ effects, which reduces the availability of the lone pair on nitrogen, thereby decreasing basic strength.
(D) $-CH_3$: It shows +I effect and increases basicity.
Step 3: Conclusion.
The $-NO_2$ group decreases the basic strength of substituted aniline.