What is mutarotation ?

Explanation

### Step-by-Step Solution:

1. **Definition of Mutarotation**:
Mutarotation is defined as the change in the specific rotation of an optically active compound when it is dissolved in a solution over time. This phenomenon occurs due to the interconversion of different anomeric forms of the compound.

2. **Optically Active Compounds**:
Optically active compounds are substances that can rotate plane-polarized light. This property is crucial for understanding mutarotation, as the specific rotation changes during the process.

3. **Example of Reducing Sugars**:
A common example of mutarotation is observed in reducing sugars, such as glucose. When glucose is dissolved in water, it exhibits mutarotation.

4. **Equilibrium of Forms**:
In an aqueous solution, glucose exists in three forms:
- Alpha-D-glucose
- Beta-D-glucose
- Open-chain form

5. **Proportions of Forms**:
The equilibrium between these forms results in specific proportions:
- Beta-D-glucose: 64%
- Alpha-D-glucose: 36%
- Open-chain form: 0.02% (negligible)

6. **Conclusion**:
The change in the specific rotation of glucose over time, as it equilibrates between these forms, is what we refer to as mutarotation.