Textbook Question
The mechanism of glycoside formation is the same as the second part of the mechanism for acetal formation. Propose a mechanism for the formation of methyl β-D-glucopyranoside.
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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 23
Predict the products obtained when d-galactose reacts with each reagent.(a) Br2 and H2O
Verified step by step guidance1
Identify the functional groups present in D-galactose. D-galactose is an aldose sugar, meaning it contains an aldehyde group (-CHO) at the anomeric carbon and multiple hydroxyl (-OH) groups.
Understand the reactivity of Br₂ in H₂O. Bromine in water is a mild oxidizing agent that selectively oxidizes aldehydes to carboxylic acids without affecting the hydroxyl groups.
Write the reaction mechanism. The aldehyde group (-CHO) of D-galactose reacts with Br₂ in H₂O to form a carboxylic acid group (-COOH), converting the sugar into its corresponding aldonic acid.
Determine the product. The oxidation of the aldehyde group in D-galactose results in the formation of D-galactonic acid, where the aldehyde is replaced by a carboxylic acid group.
Verify the stereochemistry. Since the reaction only affects the aldehyde group and does not alter the stereochemistry of the other chiral centers, the stereochemistry of the sugar remains unchanged.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
D-Galactose Structure
D-galactose is a six-carbon aldose sugar with a specific stereochemistry. It contains an aldehyde functional group and multiple hydroxyl groups, which are crucial for its reactivity. Understanding its structure helps predict how it will interact with reagents, particularly in oxidation and substitution reactions.
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Monosaccharides - D and L Isomerism
Oxidation Reactions
Oxidation reactions involve the loss of electrons or an increase in oxidation state, often resulting in the conversion of alcohols to carbonyl compounds. In the case of D-galactose reacting with Br2 and H2O, the aldehyde group can be oxidized to a carboxylic acid, leading to specific product formation. Recognizing the nature of the oxidizing agent is essential for predicting the outcome.
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Halogenation of Sugars
Halogenation refers to the introduction of halogen atoms into organic compounds. When D-galactose reacts with bromine in the presence of water, it can undergo bromination at the hydroxyl groups or the aldehyde carbon, leading to the formation of brominated sugar derivatives. Understanding the mechanism of halogenation is key to predicting the products of this reaction.
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Related Practice
Textbook Question
Draw the structures of the compound ethyl β-D-ribofuranoside.
Allose is the C3 epimer of glucose, and ribose is the C2 epimer of arabinose.
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Textbook Question
Show the products that result from hydrolysis of amygdalin in dilute acid. Can you suggest why amygdalin might be toxic to tumor (and possibly other) cells?
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Textbook Question
Draw the structures of the compound α-D-allopyranose.
Allose is the C3 epimer of glucose, and ribose is the C2 epimer of arabinose.
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Textbook Question
Treatment of either anomer of fructose with excess ethanol in the presence of a trace of HCl gives a mixture of the α and β anomers of ethyl-D-fructofuranoside. Draw the starting materials, reagents, and products for this reaction. Circle the aglycone in each product.
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Textbook Question
Show the product that results when fructose is treated with an excess of methyl iodide and silver oxide.