Which of the following does not exist as a Zwitter ion

Options

A. Glycine
B. Glutamic acid
C. Sulphanilic acid
D. p-aminobenzoic acid

Explanation

To determine which of the following compounds does not exist as a zwitterion, we need to understand what a zwitterion is and analyze the structures of the compounds mentioned.

### Step-by-Step Solution:

1. **Understanding Zwitterions**:
- A zwitterion is a molecule that has both positive and negative charges but is overall electrically neutral. This typically occurs in amino acids where the amino group (-NH2) can accept a proton (H+) to become -NH3+, and the carboxylic acid group (-COOH) can lose a proton to become -COO-.

2. **Analyzing Glycine**:
- Glycine (NH2-CH2-COOH) is an alpha amino acid. In an aqueous solution, it exists as a zwitterion:
- The amino group becomes positively charged (-NH3+).
- The carboxylic group becomes negatively charged (-COO-).
- Therefore, glycine exists as a zwitterion.

3. **Analyzing Glutamic Acid**:
- Glutamic acid (NH2-CH2-CH2-COOH) is also an amino acid. It has an additional carboxylic acid group compared to glycine.
- In solution, it can also exist as a zwitterion:
- One carboxylic group loses a proton (-COO-), while the amino group gains a proton (-NH3+).
- Thus, glutamic acid exists as a zwitterion.

4. **Analyzing Sulfanilic Acid**:
- Sulfanilic acid (C6H4(NH2)(SO3H)) has an amino group and a sulfonic acid group.
- In solution, the amino group can be protonated (-NH3+) and the sulfonic acid group can lose a proton (-SO3-).
- Therefore, sulfanilic acid also exists as a zwitterion.

5. **Analyzing Para-Aminobenzene (Aniline)**:
- Para-aminobenzene (C6H4(NH2)) does not have a carboxylic acid group to lose a proton. It only has an amino group.
- In aqueous solution, it cannot form a zwitterion because it lacks the necessary acidic group to provide a negative charge.
- Therefore, para-aminobenzene does not exist as a zwitterion.

### Conclusion:
The compound that does not exist as a zwitterion is **Para-amino-benzene**.