Which of the following compound exists as a dipolar ion ?

Options

A. Sulphamic acid
B. p -aminobenzonic acid
C. sulphanilic acid
D. p- aminophenol

Answer

To determine which of the given compounds exists as a dipolar ion (or zwitterion), we need to understand the characteristics of zwitterions. A zwitterion is a molecule that has both a positive and a negative charge, but is overall neutral. This typically occurs in compounds that contain both an acidic group (like a carboxyl group) and a basic group (like an amino group).

### Step-by-Step Solution:

1. **Identify the Characteristics of Zwitterions**:
- A zwitterion must contain both a positively charged group (usually an ammonium ion, -NH3⁺) and a negatively charged group (usually a carboxylate ion, -COO⁻).
- The presence of these two functional groups in the same molecule is essential for the formation of a zwitterion.

2. **Examine the Given Compounds**:
- **Sulfamic Acid**: Contains -SO3H and -NH2 groups. It does not have a carboxyl group, so it cannot form a zwitterion.
- **Para-Aminobenzoic Acid**: Contains -COOH (carboxyl group) and -NH2 (amino group). This compound can exist as a zwitterion because it has both acidic and basic groups.
- **Para-Aminophenol**: Contains -OH (hydroxyl group) and -NH2 (amino group). This does not form a zwitterion as it lacks a carboxyl group.
- **Sulfanilic Acid**: Contains -SO3H (sulfonic acid) and -NH2 (amino group). This compound can also exist as a zwitterion because it has both acidic and basic groups.

3. **Conclusion**:
- Among the compounds analyzed, **Sulfanilic Acid** and **Para-Aminobenzoic Acid** can exist as zwitterions. However, the question asks for a single answer, and based on the context, **Sulfanilic Acid** is highlighted as the correct answer in the video transcript.

### Final Answer:
The compound that exists as a dipolar ion (zwitterion) is **Sulfanilic Acid**.

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