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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3:55 minutes

Problem 21c

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.

Verified step by step guidance

Understand the problem: The task is to draw the structure of ethyl β-D-ribofuranoside. This involves understanding the structure of ribose, its furanose form, and the β-glycosidic bond with an ethyl group. Additionally, the problem mentions epimers, which are sugars that differ in configuration at a single stereogenic center.

Step 1: Recall the structure of D-ribose. D-ribose is a five-carbon aldose sugar (an aldopentose) with the molecular formula C₅H₁₀O₅. In its Fischer projection, the hydroxyl groups on carbons 2, 3, and 4 are arranged as follows: OH on the right (C2), OH on the right (C3), and OH on the right (C4).

Step 2: Convert D-ribose into its furanose form. In aqueous solution, D-ribose cyclizes to form a five-membered ring (furanose) by the reaction of the hydroxyl group on C4 with the aldehyde group on C1. This forms a hemiacetal. The β-anomer is formed when the hydroxyl group on C1 is oriented above the plane of the ring in the Haworth projection.

Step 3: Add the ethyl group to form ethyl β-D-ribofuranoside. The ethyl group replaces the hydrogen of the hydroxyl group on C1, forming a glycosidic bond. This results in the structure of ethyl β-D-ribofuranoside, where the ethyl group is attached to the anomeric carbon (C1) and the β-configuration is maintained.

Step 4: Verify the stereochemistry and draw the final structure. Ensure that the stereochemistry of the hydroxyl groups on C2, C3, and C4 matches that of D-ribose in the furanose form. The β-glycosidic bond should have the ethyl group pointing above the plane of the ring in the Haworth projection.

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Key Concepts

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

Furanose Structure

Furanose refers to a five-membered ring structure formed by the cyclization of sugars. In the case of ribofuranoside, the ribose sugar forms a furanose ring when the hydroxyl group on the C1 carbon reacts with the hydroxyl group on the C4 carbon. Understanding this structure is crucial for drawing the correct representation of ethyl b-D-ribofuranoside.

Epimerization

Epimerization is the process by which two sugars differ in configuration at only one specific carbon atom. In the context of the question, allose is an epimer of glucose at the C3 position, while ribose is an epimer of arabinose at the C2 position. Recognizing these relationships helps in understanding the structural differences between these sugars.

Glycosidic Bond Formation

A glycosidic bond is formed when a sugar reacts with an alcohol, resulting in the formation of an ether linkage. In the case of ethyl b-D-ribofuranoside, the hydroxyl group on the anomeric carbon of ribofuranose reacts with ethanol to form this bond. This concept is essential for accurately depicting the final structure of the compound.

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Related Practice

Textbook Question

4-Hydroxy- and 5-hydroxyaldehydes exist primarily as cyclic hemiacetals. Draw the structure of the cyclic hemiacetal formed by each of the following:

b. 4-hydroxypentanal

Textbook Question

4-Hydroxy- and 5-hydroxyaldehydes exist primarily as cyclic hemiacetals. Draw the structure of the cyclic hemiacetal formed by each of the following:

c. 5-hydroxypentanal

Textbook Question

4-Hydroxy- and 5-hydroxyaldehydes exist primarily as cyclic hemiacetals. Draw the structure of the cyclic hemiacetal formed by each of the following:

d. 4-hydroxyheptanal

Textbook Question

Draw the structures of the compound methyl α-D-galactopyranoside.

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

(a) β-D-mannopyranose (the C2 epimer of glucose).

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