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 27a
Draw the expected product of the reaction of the following sugars with excess methyl iodide and silver oxide.
(a) α-D-fructofuranose
Verified step by step guidance1
Identify the functional groups in α-D-fructofuranose. It contains hydroxyl (-OH) groups and a ketone group. These are the reactive sites in the molecule.
Understand the role of the reagents: Methyl iodide (CH₃I) is a methylating agent, and silver oxide (Ag₂O) acts as a base to facilitate the methylation reaction. The hydroxyl groups will be converted into methoxy (-OCH₃) groups.
Determine the stereochemistry of α-D-fructofuranose. The 'α' designation indicates that the anomeric hydroxyl group (on carbon-2) is in the axial position (downward in the Haworth projection). This stereochemistry will be retained in the product.
React each hydroxyl group with excess methyl iodide and silver oxide. Each hydroxyl group will be replaced with a methoxy group (-OCH₃). The ketone group on carbon-2 remains unaffected by this reaction.
Draw the final structure of the product. Ensure that all hydroxyl groups are replaced with methoxy groups, and the stereochemistry of the molecule is preserved. The product will be a fully methylated derivative of α-D-fructofuranose.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Glycosylation Reaction
Glycosylation is a chemical reaction where a sugar molecule reacts with an alcohol or another sugar to form a glycosidic bond. In this context, the reaction of sugars with methyl iodide involves the substitution of a hydroxyl group on the sugar with a methyl group, leading to the formation of methyl glycosides. Understanding this reaction is crucial for predicting the product formed when sugars react with methyl iodide.
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General Reaction
Reactivity of Sugars
Sugars, particularly in their cyclic forms, can exhibit different reactivities based on their functional groups. In the case of a-D-fructofuranose, the presence of hydroxyl groups makes it susceptible to nucleophilic substitution reactions. Recognizing the specific functional groups and their positions on the sugar is essential for determining how the sugar will react with reagents like methyl iodide.
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Role of Silver Oxide
Silver oxide (Ag2O) acts as a base in organic reactions, facilitating the deprotonation of alcohols to form alkoxide ions, which are stronger nucleophiles. In the reaction with methyl iodide, silver oxide helps to enhance the nucleophilicity of the hydroxyl groups on the sugar, promoting the substitution reaction. Understanding the role of silver oxide is important for predicting the efficiency and outcome of the reaction.
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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
Textbook Question
What do the results of parts (a) and (b) imply about the hemiacetal structure of fructose?
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
Show what happens when the product of part (a) is hydrolyzed using dilute acid.
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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