Question

Which of the following will not show mutarotation?

• A. Maltose
• B. Lactose
• C. Glucose
• D. Sucrose

Hint:

Mutarotation is characteristic of reducing sugars, which contain a free aldehyde or ketone group capable of undergoing interconversion between anomeric forms. Non-reducing sugars like sucrose do not exhibit this behavior.

Answer 1

The Correct Option is D

To determine which sugar will not show mutarotation, we must first understand what mutarotation is. Mutarotation is the change in specific rotation that occurs when an α-anomer equilibrates with a β-anomer. This phenomenon typically occurs in carbohydrates that contain hemiacetal or hemiketal functionalities. This is because these groups can open to form an aldehyde or ketone and then reclose to form either of the crytals mentioned above.

Let's analyze the options:

• Maltose: It consists of two glucose units, has a free hemiacetal OH group, and hence can undergo mutarotation.
• Lactose: Composed of glucose and galactose units with a free hemiacetal group, allowing for mutarotation.
• Glucose: A simple sugar with a free hemiacetal OH group in its cyclic form. Glucose can easily show mutarotation since it interconverts between α and β forms in solution.
• Sucrose: A disaccharide of glucose and fructose linked by their anomeric carbons, forming a glycosidic bond. Due to the absence of a free hemiacetal OH group, sucrose does not exhibit mutarotation.

Conclusion: Sucrose will not show mutarotation since it lacks a free hemiacetal group that can open and close in solution.