The two cyclic hemiacetal forms of glucose differing only in the configuration of the hydroxyl group at C-1 are called

Options

A. (a) Anomers
B. (b) Enantiomers
C. (c) Epimers
D. (d) Metamers

Answer

To answer the question regarding the two cyclic hemiacetal forms of glucose that differ only in the configuration of the hydroxyl group at C-1, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Hemiacetals**:
- A hemiacetal is formed when an aldehyde reacts with an alcohol. In the case of glucose, the aldehyde group at C-1 reacts with the hydroxyl group at C-5 to form a cyclic structure.

2. **Identifying the Cyclic Forms**:
- Glucose can exist in two cyclic forms: alpha (α) and beta (β). These forms arise from the reaction of the carbonyl group (C=O) with a hydroxyl group (–OH) to form a ring structure.

3. **Analyzing the Configuration at C-1**:
- The difference between the two cyclic forms lies in the orientation of the hydroxyl group (-OH) attached to the anomeric carbon (C-1).
- In the alpha form (α-D-glucose), the hydroxyl group at C-1 is positioned downward (trans to the CH2OH group).
- In the beta form (β-D-glucose), the hydroxyl group at C-1 is positioned upward (cis to the CH2OH group).

4. **Defining Anomers**:
- The two cyclic forms of glucose that differ only in the configuration around the anomeric carbon (C-1) are known as anomers.
- Anomers are a specific type of epimer that differ in configuration at the anomeric carbon.

5. **Conclusion**:
- Therefore, the two cyclic hemiacetal forms of glucose differing only in the configuration of the hydroxyl group at C-1 are called **anomers**.

### Final Answer:
The two cyclic hemiacetal forms of glucose differing only in the configuration of the hydroxyl group at C-1 are called **anomers**.