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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7:11 minutes

Problem 57

Textbook Question

Draw the mechanism for the last step in the Kiliani-Fischer synthesis.

Verified step by step guidance

Identify the last step in the Kiliani-Fischer synthesis: The last step involves the conversion of the cyanohydrin intermediate into an aldose sugar through hydrolysis and tautomerization.

Begin by hydrolyzing the cyanohydrin group (-C≡N) into a carboxylic acid (-COOH) using acidic water (H₃O⁺). This step breaks the triple bond and introduces two oxygen atoms to form the carboxylic acid.

Recognize that the carboxylic acid group (-COOH) is then reduced to an aldehyde (-CHO) using a mild reducing agent, such as hydrogen gas (H₂) with a palladium catalyst (Pd/BaSO₄). This step is known as partial reduction.

Understand that the resulting compound is a mixture of two epimeric aldoses (diastereomers) due to the creation of a new stereocenter at the carbon adjacent to the aldehyde group. This is a key feature of the Kiliani-Fischer synthesis.

Draw the full mechanism, showing the hydrolysis of the cyanohydrin, the reduction of the carboxylic acid to an aldehyde, and the formation of the two epimeric aldoses. Use curved arrows to indicate electron movement in each step of the mechanism.

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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 method for elongating carbon chains in carbohydrates. It involves the addition of a cyanide ion to an aldose sugar, resulting in a new carbon-carbon bond. This process allows for the formation of higher aldehydes from simpler sugars, which is crucial in carbohydrate chemistry.

Mechanism of Nucleophilic Addition

The last step of the Kiliani-Fischer synthesis involves nucleophilic addition, where a nucleophile (cyanide ion) attacks the electrophilic carbon of the carbonyl group in the sugar. This step is essential for forming the new carbon-carbon bond, leading to the production of a cyanohydrin intermediate, which can further undergo hydrolysis to yield the desired sugar derivative.

Stereochemistry in Sugars

Understanding stereochemistry is vital in the Kiliani-Fischer synthesis, as sugars have multiple chiral centers. The addition of the cyanide ion can lead to the formation of diastereomers, which are different compounds with distinct properties. Recognizing the stereochemical outcomes of the reaction is important for predicting the final structure of the synthesized sugar.

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Related Practice

Textbook Question

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

a. D-xylose

Textbook Question

D-Xylose and D-lyxose are formed when d-threose undergoes a Kiliani–Fischer synthesis. D-Xylose is oxidized to an optically inactive aldaric acid, whereas D-lyxose forms an optically active aldaric acid. What are the structures of D-xylose and D-lyxose?

Textbook Question

Predict the products obtained when D-galactose reacts with each reagent.

(j) (1) KCN/HCN; (2) H₂, Pd/BaSO₄; (3) H₃O⁺

Textbook Question

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

b. L-threose

Textbook Question

Predict the product of each of the following reactions.

(b)

Open Question

Predict the product(s) for the following reaction. Provide the mechanism of the imine hydrolysis step if required.

Textbook Question