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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5:43 minutes

Problem 67

Textbook Question

Starting with a Fischer projection of d-glucose (and other sugars), switch only the stereocenter that gave it the designation of d. What new sugar have you made? [Hint: The answer is not l-glucose.]

Verified step by step guidance

Identify the stereocenter in the Fischer projection of d-glucose that determines its 'd' designation. This is typically the chiral center farthest from the aldehyde group (C-5 in glucose).

Understand that the 'd' or 'l' designation is based on the orientation of the hydroxyl group (-OH) on the chiral center farthest from the carbonyl group. In d-glucose, this hydroxyl group is on the right side in the Fischer projection.

Switch the configuration of this specific stereocenter (C-5) from 'd' to its opposite configuration. This means changing the position of the hydroxyl group from the right to the left in the Fischer projection.

Recognize that changing the configuration of this stereocenter does not result in l-glucose, but rather an epimer of glucose. An epimer is a sugar that differs from another sugar in the configuration at only one chiral center.

Determine the name of the new sugar formed by this change. Since only the C-5 stereocenter is altered, the new sugar is d-mannose, which is an epimer of d-glucose at C-2.

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Key Concepts

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

Fischer Projection

A Fischer projection is a two-dimensional representation of a three-dimensional organic molecule by projection. It is particularly useful for depicting carbohydrates and amino acids. In this projection, the carbon chain is drawn vertically, with the most oxidized carbon at the top, and horizontal lines represent bonds coming out of the plane towards the viewer.

Stereochemistry

Stereochemistry involves the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In sugars, stereochemistry is crucial as it determines the sugar's identity and properties. The 'd' or 'l' designation in sugars refers to the configuration of the chiral center farthest from the carbonyl group, which is critical in determining the sugar's stereochemical identity.

Epimers

Epimers are sugars that differ only in the configuration around one specific carbon atom. In the context of the question, changing the stereocenter that gives d-glucose its 'd' designation results in an epimer of glucose. This change does not produce l-glucose but rather another sugar, such as d-mannose or d-galactose, depending on which stereocenter is altered.

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