Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

28. Carbohydrates

Monosaccharides - D and L Isomerism

Organic Chemistry

28. Carbohydrates

Monosaccharides - D and L Isomerism

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8:08 minutes

Problem 6c,d

Textbook Question

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.

Verified step by step guidance

Step 1: Understand the concept of epimers. Epimers are stereoisomers that differ in configuration at only one specific chiral center. For example, the C3 epimer of D-talose means that the configuration at the third carbon (C3) is inverted compared to D-talose.

Step 2: Draw the structure of D-talose. D-talose is an aldohexose (a six-carbon sugar with an aldehyde group at C1). Its stereochemistry at each chiral center (C2, C3, C4, and C5) follows the D-series convention. Refer to Figure 23-3 for the exact stereochemistry of D-talose.

Step 3: Modify the structure of D-talose to create D-idose, the C3 epimer. To do this, invert the stereochemistry at C3 while keeping the configurations at C2, C4, and C5 unchanged. Ensure the hydroxyl group (-OH) at C3 is flipped to the opposite side.

Step 4: For part d, draw the structure of D-xylose, which is an aldopentose (a five-carbon sugar with an aldehyde group at C1). Identify the stereochemistry at C2, C3, and C4 based on the D-series convention.

Step 5: Modify the structure of D-xylose to create the C4 'epimer.' Invert the stereochemistry at C4 while keeping the configurations at C2 and C3 unchanged. Notice that this inversion results in an L-series sugar. Compare the resulting structure to known sugars and identify its correct name as L-arabinose, the enantiomer of D-arabinose.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Epimers

Epimers are a specific type of diastereomer that differ in configuration at only one stereogenic center. In the context of sugars, epimers are important for understanding the structural variations between different monosaccharides. For example, d-idose and D-talose are epimers because they differ at one carbon atom, which affects their chemical properties and biological functions.

C3 and C4 Epimers

C3 and C4 epimers refer to the specific positions of the stereogenic centers that differ between two sugars. C3 epimers differ at the third carbon atom, while C4 epimers differ at the fourth carbon. This distinction is crucial for identifying and drawing the correct structures of sugars, as it influences their nomenclature and reactivity.

L-series Sugars

L-series sugars are a classification of sugars based on their stereochemistry, specifically the configuration of the chiral carbon farthest from the aldehyde or ketone group. In the case of D-xylose, its C4 epimer is an L-series sugar, which means it has a different spatial arrangement at the fourth carbon. Understanding this classification helps in naming and distinguishing between enantiomers and their respective properties.

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