Question

Which of the following will not show mutarotation?

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

Answer 1

The Correct Option is D

To answer the question "Which of the following will not show mutarotation?" we need to understand the concept of mutarotation in carbohydrates.

Mutarotation is the change in the optical rotation because of the change in equilibrium between two anomers, when the corresponding stereocenters interconvert. This phenomenon is observed in carbohydrates that have a free aldehydic or ketonic group, typically hexoses like glucose, or disaccharides like maltose, which are capable of ring-opening to form an open-chain form.

1. Glucose - Glucose is a monosaccharide with a free aldehyde group in its open-chain form. It exhibits mutarotation as it can convert between its α and β anomeric forms.
2. Maltose - Maltose is a disaccharide consisting of two glucose molecules linked by an α(1→4) glycosidic bond. It has a free aldehyde group as one of the glucose rings can open to form an open-chain aldehyde structure, allowing mutarotation.
3. Lactose - Lactose is another disaccharide made up of glucose and galactose linked by a β(1→4) bond. Similar to maltose, it can also undergo mutarotation due to the presence of a free aldehyde group in its open-chain form.
4. Sucrose - Sucrose is a disaccharide consisting of glucose and fructose linked by a glycosidic bond connecting the anomeric carbon of glucose (C1) to the anomeric carbon of fructose (C2). Both glycosidic positions are occupied, meaning sucrose does not have free aldehylic or ketonic groups to undergo ring opening and thus cannot exhibit mutarotation.

Hence, the correct answer is Sucrose, as it does not show mutarotation due to the absence of a free anomeric carbon that can participate in ring-opens, unlike the other options.