Textbook Question
Draw the expected product of the reaction of the following sugars with excess methyl iodide and silver oxide.
(b) β-D-galactopyranose
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 28a
Predict the products formed when the following sugars react with excess acetic anhydride and pyridine.
(a) α-D-glucopyranose
Verified step by step guidance1
Identify the functional groups present in α-D-glucopyranose. It contains hydroxyl (-OH) groups on the sugar ring and an anomeric hydroxyl group at the C1 position.
Understand the role of acetic anhydride and pyridine. Acetic anhydride is an acetylating agent that reacts with hydroxyl groups to form acetate esters, while pyridine acts as a base to neutralize the byproduct (acetic acid) and facilitate the reaction.
Determine the number of hydroxyl groups available for reaction. In α-D-glucopyranose, there are five hydroxyl groups: one at the anomeric carbon (C1) and four on the other carbons of the sugar ring.
Predict the reaction outcome. Each hydroxyl group will react with acetic anhydride to form an acetate ester. The product will be a fully acetylated sugar, where all hydroxyl groups are replaced with acetate groups (-OCOCH₃).
Draw the structure of the product. The α-D-glucopyranose will now have acetate groups attached to all five positions where hydroxyl groups were originally present, maintaining the pyranose ring structure.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acetic Anhydride Reactivity
Acetic anhydride is a powerful acetylating agent used to introduce acetyl groups into organic molecules. In the presence of a base like pyridine, it reacts with hydroxyl groups on sugars, converting them into acetylated derivatives. This reaction is crucial for modifying sugars to improve their solubility and stability in various chemical processes.
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Anhydride Nomenclature
Pyridine as a Catalyst
Pyridine acts as a base and catalyst in the acetylation reaction, facilitating the nucleophilic attack of the sugar's hydroxyl groups on the acetic anhydride. Its basicity helps to deprotonate the hydroxyl groups, making them more nucleophilic and enhancing the reaction rate. Understanding the role of pyridine is essential for predicting the outcome of the reaction.
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Sugar Structure and Reactivity
The structure of sugars, particularly their anomeric carbon and hydroxyl groups, significantly influences their reactivity. In the case of α-D-glucopyranose, the configuration at the anomeric carbon determines the specific products formed during acetylation. Recognizing how different hydroxyl groups on the sugar can react helps in predicting the final acetylated products.
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Related Practice
Textbook Question
Propose a mechanism for methylation of any one of the hydroxy groups of methyl α-D-glucopyranoside, using NaOH and dimethyl sulfate.
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Textbook Question
Draw the expected product of the reaction of the following sugars with excess methyl iodide and silver oxide.
(a) α-D-fructofuranose
Textbook Question
Show that Ruff degradation of D-mannose gives the same aldopentose (D-arabinose) as does D-glucose.
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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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