Question

Which of the following is the correct structure of L-fructose?

• A.
• B.
• C.
• D.

Hint:

Remember the structure of L-fructose, including the position of the hydroxyl groups and the orientation of the chiral centers.

Answer 1

The Correct Option is C

Answer 2

To determine the correct structure of L-fructose, we must understand the stereochemistry and structure of sugars, particularly their D and L configurations.

Fructose is a ketohexose, meaning it has a ketone group at the second carbon and has six carbon atoms. The difference between D-fructose and L-fructose lies in the configuration of the asymmetric carbon atoms, specifically the chiral centers.

The D/L notation does not refer to the direct spatial arrangement (dextrorotatory or levorotatory) but rather to the stereochemistry, which relates to the structure of glyceraldehyde. In sugars, the D or L configuration is determined by the orientation of the hydroxyl group on the last chiral carbon (farthest from the ketone group) in the Fischer projection:

• If the hydroxyl group is on the right, it is a D-sugar.
• If the hydroxyl group is on the left, it is an L-sugar.

For L-fructose, the hydroxyl group on the last chiral carbon should be on the left in its Fischer projection.

Let's examine the given options to identify the correct structure of L-fructose:

The correct image, showing the hydroxyl group on the last chiral carbon of L-fructose positioned to the left, matches the structure in the third option:

Therefore, the correct structure for L-fructose is represented by the third option. This aligns with the characteristic organization of L-sugars.