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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5:00 minutes

Problem 11

Textbook Question

The carbonyl group in D-galactose may be isomerized from C1 to C2 by brief treatment with dilute base (by the enediol rearrangement). The product is the C4 epimer of fructose. Draw the furanose structure of the product.

Verified step by step guidance

Identify the starting molecule, D-galactose, which is an aldohexose (a six-carbon sugar with an aldehyde group at C1). Understand that the enediol rearrangement involves the migration of the carbonyl group from C1 to C2 under basic conditions.

Recognize that the enediol rearrangement proceeds through the formation of an enediol intermediate. The base abstracts a proton from the alpha-carbon (C2), forming a resonance-stabilized enediol structure where the double bond is between C1 and C2, and hydroxyl groups are attached to both carbons.

After the enediol intermediate is formed, the carbonyl group reforms, but this time at C2 instead of C1. This converts the sugar from an aldose (aldehyde-containing sugar) to a ketose (ketone-containing sugar). The resulting ketose is D-fructose.

Determine the C4 epimer of D-fructose. An epimer is a stereoisomer that differs in configuration at only one stereogenic center. The C4 epimer of D-fructose is D-psicose, which has the opposite stereochemistry at C4 compared to D-fructose.

Draw the furanose structure of D-psicose. In the furanose form, the sugar adopts a five-membered ring structure. The ketone group at C2 reacts with the hydroxyl group at C5 to form a cyclic hemiketal. Ensure the stereochemistry at C4 reflects the epimeric difference from D-fructose.

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Key Concepts

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

Carbonyl Group and Isomerization

The carbonyl group (C=O) is a functional group found in aldehydes and ketones, playing a crucial role in organic reactions. Isomerization refers to the process where a compound is transformed into another compound with the same molecular formula but a different structure. In the context of D-galactose, the carbonyl group can shift from the C1 position to the C2 position, leading to the formation of an enediol intermediate, which is essential for the rearrangement.

Enediol Rearrangement

The enediol rearrangement is a chemical reaction where a carbonyl compound is converted into an enediol, which is a compound containing both a double bond and a hydroxyl group. This rearrangement allows for the migration of the carbonyl group, facilitating the formation of different isomers. In this case, the enediol form of D-galactose allows for the isomerization to produce a C4 epimer of fructose.

Furanose Structure

Furanose refers to a five-membered ring structure formed by the cyclization of sugars, particularly those containing a carbonyl group. In the case of the C4 epimer of fructose, the furanose form is generated when the hydroxyl group on C2 reacts with the carbonyl carbon, resulting in a stable cyclic structure. Understanding the furanose structure is essential for visualizing the final product of the isomerization process described in the question.

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Related Practice

Textbook Question

Two structures of the sugar fructose are shown next. The cyclic structure predominates in aqueous solution.

(a) Number the carbon atoms in the cyclic structure. What is the functional group at C2 in the cyclic form?

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

Textbook Question

Draw the mechanism for the interconversion of α-D-glucose and β-D-glucose in dilute HCl.

Textbook Question

Allose is the C3 epimer of glucose. Draw the cyclic hemiacetal form of D-allose, first in the chair conformation and then in the Haworth projection.

Textbook Question

Ribose, the C2 epimer of arabinose, is most stable in its furanose form. Draw D-ribofuranose.

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.

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