Question

The order of basic strength among the following amines is: Aniline, Methylamine, Dimethylamine, and Ammonia.

• A. Dimethylamine \(>\) Methylamine \(>\) Ammonia \(>\) Aniline
• B. Methylamine \(>\) Dimethylamine \(>\) Ammonia \(>\) Aniline
• C. Ammonia \(>\) Methylamine \(>\) Dimethylamine \(>\) Aniline
• D. Aniline \(>\) Ammonia \(>\) Methylamine \(>\) Dimethylamine

Hint:

Electron donating groups increase basicity, while resonance delocalization decreases basicity because the lone pair becomes less available.

Answer 1

The Correct Option is A

Concept:
Basicity of amines depends upon the availability of the lone pair of electrons on nitrogen for donation. Factors affecting basicity:
• \(+I\) effect of alkyl groups increases electron density on nitrogen.
• Resonance delocalization decreases availability of lone pair.
• Solvation effects also influence stability.

Step 1: Compare aliphatic amines with ammonia.
Alkyl groups donate electrons due to the inductive effect. Thus: \[ \text{Dimethylamine} > \text{Methylamine} > \text{Ammonia} \] because dimethylamine has two electron-releasing methyl groups.

Step 2: Analyze aniline.
In aniline: \[ \text{C}_6\text{H}_5\text{NH}_2 \] The lone pair on nitrogen participates in resonance with the benzene ring: \[ \text{N lone pair} \rightarrow \text{benzene ring} \] Hence the lone pair becomes less available for protonation. Therefore, aniline is less basic than ammonia.

Step 3: Final order.
Combining all effects: \[ \boxed{\text{Dimethylamine} > \text{Methylamine} > \text{Ammonia} > \text{Aniline}} \]