Mutarotation in Carbohydrates

Mutarotation is the process by which the specific rotation of an optically active compound changes over time. It occurs in monosaccharides, which are simple sugars, due to the interconversion between two anomeric forms - the α-anomer and the β-anomer. Mutarotation is not observed in disaccharides like sucrose, which is why the correct answer is option D.

Explanation:

1. Monosaccharides:
- Monosaccharides are the simplest form of carbohydrates and cannot be hydrolyzed further.
- They have a single sugar unit and are classified based on the number of carbon atoms present, such as trioses (3 carbon atoms), pentoses (5 carbon atoms), and hexoses (6 carbon atoms).
- Examples of monosaccharides include glucose, fructose, and galactose.

2. Anomeric Forms:
- Monosaccharides exist in two anomeric forms - α-anomer and β-anomer.
- The anomeric carbon is the carbon atom that is involved in the glycosidic bond formation.
- The α-anomer has the -OH group of the anomeric carbon in the axial position, while the β-anomer has the -OH group in the equatorial position.
- The interconversion between these two forms is known as mutarotation.

3. Disaccharides:
- Disaccharides are formed by the condensation of two monosaccharide units.
- They consist of a glycosidic bond between the anomeric carbon of one monosaccharide and a hydroxyl group of another monosaccharide.
- Examples of disaccharides include maltose, lactose, and sucrose.

4. Sucrose:
- Sucrose is a disaccharide composed of glucose and fructose units.
- It does not have a free anomeric carbon because the glycosidic bond is formed between the anomeric carbon of glucose and the hydroxyl group of fructose.
- As a result, sucrose does not undergo mutarotation.

Conclusion:
Mutarotation is a property observed in monosaccharides where the specific rotation changes over time due to the interconversion between the α-anomer and β-anomer. Disaccharides like sucrose, which do not have a free anomeric carbon, do not exhibit mutarotation. Therefore, option D (Sucrose) is the correct answer.