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 - Forming Cyclic Hemiacetals

Organic Chemistry

28. Carbohydrates

Monosaccharides - Forming Cyclic Hemiacetals

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1:29 minutes

Problem 47a

Textbook Question

Without referring to the chapter, draw the chair conformations of
(a) β-D-mannopyranose (the C2 epimer of glucose).

Verified step by step guidance

Understand the structure of β-D-mannopyranose: It is the C2 epimer of β-D-glucopyranose, meaning the hydroxyl group (-OH) on carbon 2 (C2) is oriented differently compared to β-D-glucopyranose. In β-D-mannopyranose, the -OH group on C2 is axial (pointing down in the chair conformation), while in β-D-glucopyranose, it is equatorial (pointing outwards).

Draw the basic pyranose ring in the chair conformation: Start by sketching a six-membered ring in the chair form, which is the most stable conformation for pyranose sugars. Label the carbons from C1 to C6 in a clockwise direction, starting with the anomeric carbon (C1).

Place the substituents on the ring: For β-D-mannopyranose, the anomeric hydroxyl group (-OH) on C1 is equatorial (pointing outwards), as it is in the β-anomer. The hydroxyl group on C2 is axial (pointing down), and the remaining hydroxyl groups on C3, C4, and C6 are equatorial. The -CH2OH group on C5 is also equatorial.

Verify the stereochemistry: Double-check the orientation of each substituent to ensure it matches the β-D-mannopyranose structure. Remember that the axial and equatorial positions alternate around the ring, and the stereochemistry of each carbon is determined by the sugar's configuration.

Draw the final chair conformation: Clearly depict the chair conformation of β-D-mannopyranose with all substituents in their correct positions. Highlight the axial -OH group on C2 to emphasize the difference from β-D-glucopyranose.

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Key Concepts

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

Chair Conformation

Chair conformation is a three-dimensional representation of cyclohexane and its derivatives, which minimizes steric strain and torsional strain. In this conformation, the carbon atoms are arranged in a staggered manner, allowing for more stable interactions between substituents. Understanding chair conformations is crucial for analyzing the spatial arrangement of atoms in cyclic sugars like mannopyranose.

Pyranose Structure

Pyranose refers to a six-membered ring structure formed by the cyclization of monosaccharides, specifically aldoses and ketoses. In the case of D-mannopyranose, the ring consists of five carbon atoms and one oxygen atom. Recognizing the pyranose structure is essential for understanding the chemical properties and reactivity of sugars, as well as their conformational variations.

Epimerization

Epimerization is the process by which two sugars differ in configuration at only one specific carbon atom. In the context of D-mannopyranose, it is the C2 epimer of glucose, meaning they differ in the orientation of the hydroxyl group at the second carbon. This concept is important for distinguishing between different sugars and understanding their biological roles and interactions.

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Related Practice

Textbook Question

Draw the structures of the compound ethyl β-D-ribofuranoside.

Allose is the C3 epimer of glucose, and ribose is the C2 epimer of arabinose.

Textbook Question

Two structures for the sugar glucose are shown on page 914. Interconversion of the open-chain and cyclic hemiacetal forms is catalyzed by either acid or base.

(a) Propose a mechanism for the cyclization, assuming a trace of acid is present.

Textbook Question

Two structures for the sugar glucose are shown on page 914. Interconversion of the open-chain and cyclic hemiacetal forms is catalyzed by either acid or base.

(b) The cyclic hemiacetal is more stable than the open-chain form, so very little of the open-chain form is present at equilibrium. Will an aqueous solution of glucose reduce Tollens reagent and give a positive Tollens test? Explain.

Textbook Question

Draw the structures of the compound α-D-allopyranose.

Allose is the C3 epimer of glucose, and ribose is the C2 epimer of arabinose.

Textbook Question

Without referring to the chapter, draw the chair conformations of

(b) α-D-allopyranose (the C3 epimer of glucose).

Textbook Question

Without referring to the chapter, draw the chair conformations of

(d) N-acetylglucosamine, glucose with the C2 oxygen atom replaced by an acetylated amino group.

Multiple Choice

In the formation of a cyclic hemiacetal from a monosaccharide, what type of reaction occurs?

Multiple Choice