Glutomic acid `(A)` has isoelectric point `3.22`
(a) What is the most likely structure of the compound at its isoelectric point ?
(b) What is the most likely structure of monosodium glutamate.
`underset(underset(underset((A))(CH_(2))-CH_(2)-COOH)(|))(H_(2)N-CH-COOH)`.

Explanation

To solve the question regarding glutamic acid and monosodium glutamate, we will break it down into two parts as specified.

### Part (a): Structure of Glutamic Acid at its Isoelectric Point

1. **Understanding the Isoelectric Point**: The isoelectric point (pI) is the pH at which a molecule carries no net electrical charge. For amino acids like glutamic acid, this typically occurs when the amino group is protonated (NH3+) and one of the carboxylic acid groups is deprotonated (COO-).

2. **Structure of Glutamic Acid**: The structure of glutamic acid can be represented as:
\[ \text{NH}_2 - \text{CH}(\text{COOH}) - \text{CH}_2 - \text{COOH} \]
Here, the first carboxylic acid group (COOH) is directly attached to the alpha carbon.

3. **Formation of Zwitterion**: At the isoelectric point (pH 3.22), glutamic acid exists predominantly as a zwitterion. In this form:
- The amino group (NH2) accepts a proton to become NH3+.
- The carboxylic acid group (COOH) loses a proton to become COO-.

4. **Final Structure of Zwitterion**:
\[ \text{NH}_3^+ - \text{CH}(\text{COO}^-) - \text{CH}_2 - \text{COOH} \]
The R group (CH2-COOH) remains unchanged as it does not participate in the proton transfer.

### Part (b): Structure of Monosodium Glutamate

1. **Understanding Monosodium Glutamate**: Monosodium glutamate (MSG) is the sodium salt of glutamic acid. In this structure, one of the carboxylic acid groups will be deprotonated and the sodium ion will associate with it.

2. **Structure of Monosodium Glutamate**: Starting from the zwitterionic form of glutamic acid, we can represent monosodium glutamate as follows:
- The COO- group (from the zwitterion) will bind to Na+.

3. **Final Structure of Monosodium Glutamate**:
\[ \text{NH}_2 - \text{CH}(\text{COO}^-) - \text{CH}_2 - \text{COO}^+ \text{Na} \]
This indicates that one of the carboxylate groups is associated with sodium, while the amino group remains protonated.

### Summary of Structures
- **Zwitterion of Glutamic Acid**:
\[ \text{NH}_3^+ - \text{CH}(\text{COO}^-) - \text{CH}_2 - \text{COOH} \]
- **Monosodium Glutamate**:
\[ \text{NH}_2 - \text{CH}(\text{COO}^-) - \text{CH}_2 - \text{COO}^+ \text{Na} \]