What best describes the following?
A)The Fischer projection of L-fructose and an anomer of D-fructose written in the Haworth projection
B)The Haworth projection of D-fructose and both anomers of D-fructose written in the Fischer projection
C)The Fischer projection of L-fructose and both anomers of L-fructose written in the Haworth projection
D) The Fischer projection of D-glucose and both anomers of D-glucose written in the Haworth projection
The Correct Answer and Explanation is :
The correct answer is D) The Fischer projection of D-glucose and both anomers of D-glucose written in the Haworth projection.
Explanation:
- Fischer Projection:
The Fischer projection, shown on the left side of the image, is a method of representing the three-dimensional structure of molecules in a two-dimensional plane. The Fischer projection in the provided image clearly depicts D-glucose due to the arrangement of hydroxyl groups (-OH) on the second, third, fourth, and fifth carbon atoms. For D-glucose, the -OH groups on the second, fourth, and fifth carbons are on the right, and the -OH on the third carbon is on the left, consistent with the D-configuration. - Haworth Projection:
The two structures on the right side of the image are the Haworth projections of D-glucose. The Haworth projection is a simplified way to show the cyclic form of sugars. These structures represent the cyclic forms of glucose, namely the α and β anomers. The anomeric carbon (the former carbonyl carbon, carbon 1) in these cyclic forms can have the -OH group positioned either below the plane of the ring (α-anomer) or above the plane of the ring (β-anomer). The diagrams show one anomer with the -OH below (α-D-glucose) and the other with the -OH above (β-D-glucose). - Determining D vs. L and Anomers:
The difference between D and L sugars in the Fischer projection is determined by the position of the -OH on the last chiral center (carbon 5 for glucose). Since it is on the right side, it indicates a D-sugar. The anomers are distinguished by the position of the -OH group at the anomeric carbon (carbon 1) after ring closure. - Elimination of Other Options:
- Option A is incorrect because L-fructose and D-fructose are not involved here.
- Option B incorrectly describes the molecules as fructose and inverts the naming of the Fischer and Haworth projections.
- Option C is incorrect because it mentions L-fructose, which is not represented in the image.
This explanation demonstrates that the structures depicted are related to D-glucose, not fructose, and certainly not the L-forms of any sugars. Thus, Option D is correct, indicating both the linear and cyclic forms of D-glucose.