(a) Draw D-allose, the C3 epimer of glucose.
(b) Draw D-talose, the C2 epimer of D-galactose.
(c) Draw D-idose, the C3 epimer of D-talose. Now compare your answers with Figure 23-3.
(d) Draw the C4 “epimer” of D-xylose. Notice that this “epimer” is actually an L-series
sugar, and we have seen its enantiomer. Give the correct name for this L-series sugar.
The Correct Answer and Explanation is :
Let’s break this down step by step and provide both the correct structures and an explanation.
(a) D-Allose (C3 Epimer of D-Glucose)
D-Allose is an aldohexose and a C3 epimer of D-Glucose. This means that the hydroxyl (-OH) group at carbon 3 is flipped compared to D-Glucose.
(b) D-Talose (C2 Epimer of D-Galactose)
D-Talose is another aldohexose and is a C2 epimer of D-Galactose. This means that the hydroxyl (-OH) group at carbon 2 is flipped compared to D-Galactose.
(c) D-Idose (C3 Epimer of D-Talose)
D-Idose is obtained by flipping the hydroxyl (-OH) group at carbon 3 of D-Talose.
(d) C4 “Epimer” of D-Xylose
D-Xylose is an aldopentose. If we attempt to create its C4 epimer, we actually obtain an L-series sugar. This sugar is L-Lyxose, which is the enantiomer of D-Lyxose.
Explanation (300 Words)
Epimers are sugars that differ only at one specific chiral center, meaning that just one carbon has an opposite configuration. For example, D-Allose is the C3 epimer of D-Glucose, meaning that they are identical except for the configuration at the third carbon.
Similarly, D-Talose is the C2 epimer of D-Galactose, so the hydroxyl (-OH) group at carbon 2 in D-Talose is flipped compared to D-Galactose.
To determine D-Idose, we take D-Talose and modify the hydroxyl (-OH) configuration at the third carbon, producing a new sugar with distinct stereochemistry. This type of systematic modification helps understand the relationship between different aldohexoses.
For D-Xylose, if we modify the hydroxyl (-OH) group at C4, we get an L-series sugar instead of a D-series sugar. This means the sugar belongs to the mirror-image family of common D-sugars. In this case, the correct name for the sugar is L-Lyxose, which is the enantiomer of D-Lyxose.
This exercise demonstrates how systematically modifying stereochemistry affects sugar classification and highlights the interrelationships between different monosaccharides.
Now, I will generate the images for these structures.
It looks like I can’t generate the molecular structures directly with RDKit here. However, I can manually illustrate the Fischer projections of D-Allose, D-Talose, D-Idose, and L-Lyxose. Let me generate an image with these structures for you.
Here is the scientific diagram featuring the Fischer projections of D-Allose, D-Talose, D-Idose, and L-Lyxose. Let me know if you need any modifications or explanations!
