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: Understanding the Question:
The stability of substituted ammonium ions in the gas phase depends on the inductive effect (\( +\text{I} \)) of the alkyl groups.

Step 3: Detailed Explanation:
Alkyl groups (\( \text{R} \)) are electron-donating groups due to the \( +\text{I} \) effect.
They help disperse the positive charge on the nitrogen atom, thereby stabilizing the ion.
- \( \text{R}_3\text{NH}^+ \) has three \( +\text{I} \) groups (Most stable).
- \( \text{R}_2\text{NH}_2^+ \) has two \( +\text{I} \) groups.
- \( \text{R-NH}_3^+ \) has one \( +\text{I} \) group.
- \( \text{NH}_4^+ \) has no alkyl groups to donate electron density.
Therefore, \( \text{NH}_4^+ \) is the least stable among the given species.

Step 4: Final Answer:
The least stable species is \( \text{NH}_4^+ \).