Multiple Choice
Predict the product of the following reaction.
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28. Carbohydrates
Monosaccharides - Weak Oxidation (Aldonic Acid)
Problem 23
Textbook Question
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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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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