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 - Cyclization

Organic Chemistry

28. Carbohydrates

Monosaccharides - Cyclization

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1:22 minutes

Problem 24

Textbook Question

Which OH groups are in the axial position in each of the following?
a. β-D-idopyranose
b. α-D-allopyranose

Verified step by step guidance

Step 1: Understand the structure of pyranose rings. Pyranose rings are six-membered cyclic structures formed by the reaction of an aldehyde or ketone group with a hydroxyl group in sugars. The axial and equatorial positions refer to the orientation of substituents on the ring relative to the plane of the ring.

Step 2: Analyze the chair conformation of b-D-idopyranose. In the beta configuration, the anomeric hydroxyl group (-OH) at the C1 position is equatorial. Identify the positions of other hydroxyl groups (C2, C3, C4, C5) and determine which are axial based on their orientation in the chair conformation.

Step 3: Analyze the chair conformation of a-D-allopyranose. In the alpha configuration, the anomeric hydroxyl group (-OH) at the C1 position is axial. Similarly, identify the positions of other hydroxyl groups (C2, C3, C4, C5) and determine which are axial based on their orientation in the chair conformation.

Step 4: Recall that axial positions alternate up and down around the ring in the chair conformation. Use the stereochemistry of each sugar to determine the specific orientation of each hydroxyl group. This requires knowledge of the sugar's Fischer projection and how it translates into the chair conformation.

Step 5: Summarize the axial hydroxyl groups for each sugar. For b-D-idopyranose, list the carbon positions where the hydroxyl groups are axial. For a-D-allopyranose, do the same. Ensure the stereochemistry is consistent with the given configurations (alpha or beta).

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Key Concepts

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

Axial and Equatorial Positions

In chair conformations of cyclohexane and related structures, substituents can occupy axial or equatorial positions. Axial substituents are oriented parallel to the axis of the ring, while equatorial substituents extend outward from the ring. This distinction affects steric interactions and stability, making it crucial for understanding the spatial arrangement of groups in cyclic compounds.

Pyranose Structure

Pyranose refers to a six-membered cyclic form of monosaccharides, derived from aldoses or ketoses. In pyranose, the anomeric carbon is typically involved in a glycosidic bond, influencing the orientation of hydroxyl (OH) groups. Understanding the structure of pyranoses is essential for determining the positions of substituents, such as OH groups, in the chair conformation.

Anomeric Effect

The anomeric effect describes the preference for certain substituents at the anomeric carbon to adopt specific orientations due to electronic interactions. In pyranoses, this effect can influence whether OH groups are positioned axially or equatorially. Recognizing the anomeric effect is important for predicting the stability and reactivity of carbohydrate structures.

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