Which pair is an example of anomers?

Options

A. `alpha`-D-glucose and `beta`-D-glucose
B. Glucose and mannose
C. Glucose and fructose
D. Fructose and sugar

Answer

To determine which pair is an example of anomers, we first need to understand what anomers are. Anomers are a type of stereoisomer found in carbohydrates that differ in configuration at the anomeric carbon, which is the carbon atom that becomes a new chiral center when a cyclic form of a sugar is formed.

### Step-by-Step Solution:

1. **Understanding Anomers**: Anomers are specific types of epimers that differ at the anomeric carbon (the first carbon in the cyclic form of a sugar). In the case of glucose, the anomeric carbon is the first carbon (C1) when it cyclizes.

2. **Drawing Alpha and Beta Glucose**:
- **Alpha Glucose**: In alpha-D-glucose, the hydroxyl group (-OH) on the anomeric carbon (C1) is positioned on the right side when the glucose molecule is drawn in the Haworth projection.
- **Beta Glucose**: In beta-D-glucose, the hydroxyl group (-OH) on the anomeric carbon (C1) is positioned on the left side in the Haworth projection.

3. **Identifying the Difference**: The only difference between alpha and beta glucose is the orientation of the hydroxyl group at the anomeric carbon (C1). In alpha glucose, it is down (or on the right), and in beta glucose, it is up (or on the left).

4. **Conclusion**: Since the only difference between alpha and beta glucose is the configuration at the anomeric carbon, they are classified as anomers. Therefore, the correct answer to the question is that the pair of alpha-D-glucose and beta-D-glucose is an example of anomers.

### Final Answer:
The pair that is an example of anomers is **alpha-D-glucose and beta-D-glucose**.