Question

Identify least stable species from following.

• A. $NH_{4}^{+}$
• B. $R-NH_{3}^{+}$
• C. $R_{2}NH_{2}^{+}$
• D. $R_{3}NH^{+}$

Hint:

In water, stability order: $NH_{4}^{+} > 1^{\circ} > 2^{\circ} > 3^{\circ}$ (based on solvation).

Answer 1

The Correct Option is D

Step 1: Concept
Stability of substituted ammonium ions in aqueous solution depends on solvation.

Step 2: Meaning
Solvation (hydration) by water molecules stabilizes the cation through hydrogen bonding with available H atoms.

Step 3: Analysis
- $NH_{4}^{+}$ has 4 H-atoms for H-bonding. - $R_{3}NH^{+}$ has only 1 H-atom for H-bonding. - Fewer H-atoms result in less extensive solvation and lower stability in water.

Step 4: Conclusion
Hence, $R_{3}NH^{+}$ is the least stable in aqueous medium. Final Answer: (D)