Question

Which of the following does not exihibit the phenomena of mutarotation?

• A. (+) Sucrose
• B. (+) Lactose
• C. (+) Maltose
• D. (-) Fructose

Answer 1

The Correct Option is A

To solve this question, we need to understand the concept of mutarotation in chemistry.

What is Mutarotation?

Mutarotation is a phenomenon observed in carbohydrates, particularly in sugars, where the optical rotation of a solution changes over time until it reaches an equilibrium value. This occurs due to the interconversion between two different anomers (e.g., alpha and beta forms) of a sugar molecule in solution.

Why does Mutarotation Occur?

Mutarotation occurs because sugars can exist in a cyclic form in aqueous solution, and these cyclic forms can open up to form a linear form and then reclose to form a different anomer. The ability to open and close the ring structure is responsible for this phenomenon.

Analysis of Given Options:

1. (+) Sucrose: Sucrose is a non-reducing sugar because the glycosidic bond in sucrose involves both the anomeric carbons of glucose and fructose. This bond prevents the ring-opening necessary for mutarotation to occur. Hence, sucrose does not exhibit mutarotation.
2. (+) Lactose: Lactose is a disaccharide that has a free anomeric carbon on the glucose portion. This free anomeric carbon can participate in ring-opening, and thus lactose can undergo mutarotation.
3. (+) Maltose: Maltose is a disaccharide that also has a free anomeric carbon, allowing the interconversion between alpha and beta forms. Thus, maltose can undergo mutarotation.
4. (-) Fructose: Fructose is a monosaccharide that can interconvert between its linear and cyclic forms, allowing mutarotation to occur in its solution.

Conclusion:

The correct answer is (+) Sucrose, as it does not exhibit mutarotation due to the absence of a free anomeric carbon necessary for interconversion between anomers.