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 - Kiliani-Fischer

Organic Chemistry

28. Carbohydrates

Monosaccharides - Kiliani-Fischer

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6: minutes

Problem 15a

Textbook Question

What monosaccharides are formed in a modified Kiliani–Fischer synthesis starting with each of the following monosaccharides?
a. D-xylose

Verified step by step guidance

Step 1: Understand the Kiliani–Fischer synthesis. This reaction is used to lengthen the carbon chain of an aldose by one carbon atom, resulting in the formation of two epimeric aldoses (diastereomers) at the new chiral center. The process involves cyanohydrin formation, hydrolysis, and reduction.

Step 2: Identify the starting monosaccharide. d-Xylose is a five-carbon aldose (aldopentose) with the structure: CHO-(CHOH)3-CH2OH. It has three chiral centers, and its stereochemistry determines the configuration of the products.

Step 3: Add one carbon to the chain. In the first step of the Kiliani–Fischer synthesis, d-xylose reacts with HCN to form a cyanohydrin intermediate. This adds a new carbon atom to the chain, creating a six-carbon compound with a nitrile group (-C≡N) at the end.

Step 4: Hydrolyze the nitrile group. The cyanohydrin is hydrolyzed under acidic conditions to form an aldonic acid, which is then reduced to an aldehyde. This step introduces a new chiral center at the second carbon from the top, resulting in two possible epimers.

Step 5: Determine the products. The two epimeric aldohexoses formed are d-glucose and d-mannose. These are distinguished by the configuration of the hydroxyl group at the new chiral center (C-2).

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Key Concepts

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

Kiliani–Fischer Synthesis

The Kiliani–Fischer synthesis is a chemical reaction used to elongate monosaccharides by adding a carbon atom to the chain. This process involves the formation of an aldehyde from a sugar, followed by the addition of cyanide to create a cyanohydrin, which can then be hydrolyzed to yield a new aldose and a new ketose. It is particularly useful for synthesizing higher sugars from simpler ones.

Monosaccharides

Monosaccharides are the simplest form of carbohydrates, consisting of single sugar units that cannot be hydrolyzed into simpler sugars. Common examples include glucose, fructose, and xylose. They serve as the building blocks for more complex carbohydrates and play crucial roles in energy metabolism and cellular functions.

Stereochemistry of Sugars

Stereochemistry refers to the spatial arrangement of atoms in molecules and is particularly important in organic chemistry for understanding the behavior of sugars. Monosaccharides can exist in different stereoisomeric forms, which can significantly affect their chemical properties and biological functions. For example, d-xylose and l-xylose are stereoisomers that differ in the configuration around one or more chiral centers.

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