Arrange the following amines in order of their increasing basic strength

(B), (C), (D), (A)

The correct answer is Option (3) → (B), (C), (D), (A)

Step 1: General principle

• The basicity of amines depends on the availability of the lone pair on nitrogen for protonation.
• Electron-donating groups (EDGs) increase basicity.
• Electron-withdrawing groups (EWGs) decrease basicity.

Step 2: Analyze each amine

1. A: (CH₃)₂NH – aliphatic tertiary amine
• EDGs: two methyl groups → increase electron density on nitrogen → high basicity.
2. B: p-Nitroaniline
• –NO₂ is a strong electron-withdrawing group → decreases lone pair availability → very low basicity.
3. C: Aniline (–NH₂ attached to benzene)
• Lone pair on nitrogen delocalizes into benzene → reduces basicity → low basicity.
4. D: p-Toluidine (p-CH₃–C₆H₄NH₂)
• –CH₃ is electron-donating → increases basicity slightly compared to aniline → moderate basicity.

Step 3: Arrange in increasing basicity

$B \,(\text{p-nitroaniline}) < C \,(\text{aniline}) < D \,(\text{p-toluidine}) < A \,(\text{dimethylamine})$

Answer: B < C < D < A