Mutarotation does not occur in:

Sucrose

The correct answer is option 3. sucrose.

Mutarotation is the change in the optical rotation that happens when a sugar solution equilibrates between different anomeric forms. This phenomenon is observed in sugars that have a free anomeric carbon, which is the carbonyl carbon that becomes chiral when the sugar forms a cyclic structure.

Anomeric Carbon:

The anomeric carbon is the carbonyl carbon in the open-chain form of the sugar that becomes chiral upon cyclization. In the cyclic forms, this carbon has two possible configurations: α (alpha) and β (beta). The interconversion between these forms leads to changes in optical rotation.

Mutarotation Process:

When a sugar like D-glucose or L-glucose is dissolved in water, it equilibrates between its α and β anomeric forms. This interconversion causes a change in the observed optical rotation of the solution, which is known as mutarotation.

Why Sucrose Does Not Exhibit Mutarotation:

Structure of Sucrose:

Sucrose is a disaccharide composed of glucose and fructose linked by a glycosidic bond. In sucrose, the anomeric carbons of both the glucose and fructose units are involved in forming this bond.

No Free Anomeric Carbon:

In sucrose, the anomeric carbons of both glucose and fructose are engaged in the glycosidic bond, making them unavailable for interconversion between α and β forms. Therefore, there is no free anomeric carbon in sucrose to undergo mutarotation.

Summary:

Mutarotation occurs in sugars with a free anomeric carbon because these sugars can interconvert between their α and β anomeric forms, leading to changes in optical rotation. Sucrose, however, does not show mutarotation because its anomeric carbons are involved in the glycosidic bond and are not available for interconversion. So, sucrose does not exhibit mutarotation due to the lack of a free anomeric carbon.