Textbook Question
Predict the products formed when the following sugars react with excess acetic anhydride and pyridine.
(a) α-D-glucopyranose
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Ch. 23 - Carbohydrates and Nucleic Acids
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 23, Problem 29
Show that Ruff degradation of D-mannose gives the same aldopentose (D-arabinose) as does D-glucose.
Verified step by step guidance1
Identify the Ruff degradation process: Ruff degradation is a method used to shorten the carbon chain of an aldose sugar by one carbon atom. It involves oxidation of the aldose to an aldonic acid, followed by decarboxylation to yield a new aldose with one fewer carbon atom.
Write the structure of D-mannose and D-glucose: Both are aldohexoses, but they differ in the stereochemistry of their hydroxyl groups. D-mannose has the hydroxyl groups on C-2 and C-3 on the same side, while D-glucose has the hydroxyl group on C-2 opposite to that on C-3.
Apply Ruff degradation to D-mannose: Oxidize D-mannose to D-mannonic acid, then decarboxylate it. The resulting aldopentose will have the same stereochemistry at C-2, C-3, and C-4 as the original D-mannose, but with one fewer carbon atom. This product is D-arabinose.
Apply Ruff degradation to D-glucose: Oxidize D-glucose to D-gluconic acid, then decarboxylate it. The resulting aldopentose will have the same stereochemistry at C-2, C-3, and C-4 as the original D-glucose, but with one fewer carbon atom. This product is also D-arabinose.
Conclude that both D-mannose and D-glucose yield the same aldopentose (D-arabinose) upon Ruff degradation, as the stereochemistry of the remaining carbons after decarboxylation is identical in both cases.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Ruff Degradation
Ruff degradation is a chemical reaction that involves the oxidative cleavage of aldoses, typically using bromine and water, to yield smaller sugar units. In this process, the aldose is first oxidized to an aldonic acid, which is then further degraded to produce a lower carbon sugar. Understanding this reaction is crucial for analyzing how D-mannose and D-glucose can both yield D-arabinose through similar pathways.
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Aldopentose
Aldopentoses are monosaccharides that contain five carbon atoms and an aldehyde functional group. D-arabinose is a specific example of an aldo-pentose, characterized by its structure and stereochemistry. Recognizing the structural features of aldopentoses is essential for understanding the products formed during the Ruff degradation of D-mannose and D-glucose.
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Stereochemistry
Stereochemistry refers to the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the context of sugars, the configuration of hydroxyl groups around the chiral centers determines the specific type of sugar produced. Analyzing the stereochemical aspects of D-mannose and D-glucose is vital to demonstrate that both can yield the same aldopentose, D-arabinose, through Ruff degradation.
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Related Practice
Textbook Question
Draw the expected product of the reaction of the following sugars with excess methyl iodide and silver oxide.
(b) β-D-galactopyranose
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Textbook Question
Ruff degradation of D-arabinose gives D-erythrose. The Kiliani–Fischer synthesis converts D-erythrose to a mixture of D-arabinose and D-ribose. Draw out these reactions, and give the structure of D-ribose.
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Textbook Question
D-Altrose is an aldohexose. Ruff degradation of D-altrose gives the same aldopentose as does degradation of D-allose, the C3 epimer of glucose. Give the structure of D-altrose.
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Textbook Question
D-Lyxose is formed by Ruff degradation of galactose. Give the structure of D-lyxose. Ruff degradation of D-lyxose gives D-threose. Give the structure of D-threose.
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Textbook Question
Predict the products formed when the following sugars react with excess acetic anhydride and pyridine.
(b) β-D-ribofuranose
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