Which of the following pairs are `C-2` epimers?

Answer

To determine which pairs are C-2 epimers, we need to analyze the structures of the given sugars and identify the configuration at the second carbon (C-2). C-2 epimers differ at the C-2 position while having the same configuration at all other chiral centers.

### Step-by-Step Solution:

1. **Identify the Sugars**: The sugars given are Allose, Altrose, Glucose, Mannose, and Glutamate.

2. **Draw the Structures**:
- **Allose**:
- Structure: CHO - H - OH - H - OH - CH2OH
- **Altrose**:
- Structure: CHO - OH - H - OH - H - CH2OH
- **Glucose**:
- Structure: CHO - H - OH - OH - H - CH2OH
- **Mannose**:
- Structure: CHO - H - OH - H - OH - CH2OH
- **Glutamate**:
- This is an amino acid and not a sugar, so we will not consider it for epimer analysis.

3. **Identify C-2 Configuration**:
- For **Allose**: C-2 has the configuration H (up) and OH (down).
- For **Altrose**: C-2 has the configuration OH (up) and H (down).
- For **Glucose**: C-2 has the configuration H (up) and OH (down).
- For **Mannose**: C-2 has the configuration OH (up) and H (down).

4. **Compare the Sugars**:
- **Allose and Altrose**: They differ at C-2 (Allose: H, Altrose: OH). Thus, they are C-2 epimers.
- **Glucose and Mannose**: They also differ at C-2 (Glucose: H, Mannose: OH). Thus, they are also C-2 epimers.

5. **Conclusion**: The pairs that are C-2 epimers are:
- Allose and Altrose
- Glucose and Mannose

### Final Answer:
The pairs that are C-2 epimers are:
- Allose and Altrose
- Glucose and Mannose