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 - Haworth Projections

Organic Chemistry

28. Carbohydrates

Monosaccharides - Haworth Projections

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3:48 minutes

Problem 22

Textbook Question

Draw the anomers of D-erythrofuranose.

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Understand the concept of anomers: Anomers are stereoisomers of cyclic sugars that differ in configuration only at the anomeric carbon (the carbon derived from the carbonyl group in the open-chain form). For D-erythrofuranose, this means we need to consider the two possible configurations (α and β) at the anomeric carbon.

Draw the open-chain form of D-erythrose: D-erythrose is an aldotetrose, meaning it has four carbons, with the first carbon being the aldehyde group. The second and third carbons are chiral, and the hydroxyl groups are arranged in the D-configuration (OH on the right in a Fischer projection).

Cyclize the molecule to form the furanose ring: D-erythrofuranose forms when the hydroxyl group on the third carbon (C3) attacks the aldehyde group on the first carbon (C1), creating a five-membered ring (furanose). This reaction forms a new chiral center at C1, the anomeric carbon.

Draw the two anomers: In the α-anomer, the hydroxyl group attached to the anomeric carbon (C1) is on the opposite side of the ring relative to the CH2OH group at C4 (down in a Haworth projection for D-sugars). In the β-anomer, the hydroxyl group at C1 is on the same side as the CH2OH group (up in a Haworth projection for D-sugars).

Label the structures: Clearly label the two structures as α-D-erythrofuranose and β-D-erythrofuranose to distinguish between the two anomers. Ensure the stereochemistry at all chiral centers is consistent with the D-configuration.

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Key Concepts

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

Anomers

Anomers are a specific type of stereoisomer found in carbohydrates, differing in configuration at the anomeric carbon, which is the carbon derived from the carbonyl group during cyclization. In the case of sugars, anomers can exist in two forms: alpha (α) and beta (β), depending on the orientation of the hydroxyl group attached to the anomeric carbon relative to the CH2OH group.

D-erythrofuranose

D-erythrofuranose is a five-membered cyclic form of the sugar D-erythrose. It is a furanose, which means it contains a furan ring structure. Understanding its structure is crucial for identifying the anomers, as the anomeric carbon in D-erythrofuranose is the carbon that was originally the carbonyl carbon in the open-chain form of the sugar.

Cyclization of Sugars

Cyclization is the process by which a linear sugar molecule forms a cyclic structure, typically through a reaction between a carbonyl group and a hydroxyl group. This process is fundamental in carbohydrate chemistry, as it leads to the formation of different anomeric forms and affects the sugar's reactivity and properties. Recognizing how cyclization occurs helps in drawing the correct anomers of D-erythrofuranose.