Textbook Question
Answer the following questions about the eight aldopentoses:
a. Which are enantiomers?
b. Which are C-2 epimers?
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Ch. 20 - The Organic Chemistry of Carbohydrates
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
Chapter 21, Problem 36c
Identify the sugar in each description.
c. A ketose that, when reduced with NaBH4, forms D-altritol and D-allitol.
Verified step by step guidance1
Identify the type of sugar described in the problem. The sugar is a ketose, meaning it contains a ketone functional group (C=O) within its structure.
Understand the reduction process. When a ketose is reduced with NaBH4 (sodium borohydride), the ketone group is converted into a secondary alcohol, resulting in the formation of two different alditols (sugar alcohols) due to the creation of a new chiral center.
Analyze the products of the reduction. The problem states that the reduction of the ketose forms d-altritol and d-allitol. These two alditols are stereoisomers, differing in the configuration of their chiral centers.
Determine the ketose that can produce these two alditols. The ketose must have a structure such that reduction at the ketone group leads to the formation of d-altritol and d-allitol. This requires analyzing the stereochemistry of the ketose and its potential reduction products.
Conclude that the ketose in question is d-psicose. When d-psicose is reduced with NaBH4, it forms d-altritol and d-allitol due to the specific arrangement of its chiral centers and the resulting stereochemistry of the reduction products.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Ketose
A ketose is a type of sugar (carbohydrate) that contains a ketone group (C=O) in its structure. Unlike aldoses, which have an aldehyde group, ketoses typically have their carbonyl group located at the second carbon atom. This structural difference influences their reactivity and the types of derivatives they can form during chemical reactions.
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Mechanism
Reduction Reaction
Reduction reactions involve the gain of electrons or hydrogen by a molecule, often resulting in the conversion of a carbonyl group (C=O) to an alcohol (C-OH). In the context of sugars, reducing agents like sodium borohydride (NaBH4) can convert ketoses into sugar alcohols, which are important in various biological and industrial processes.
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Sugar Alcohols
Sugar alcohols, or polyols, are derived from sugars through reduction, where the carbonyl group is converted into a hydroxyl group. Examples include d-altritol and d-allitol, which are formed from specific ketoses. These compounds are often used as sweeteners and have applications in food and pharmaceutical industries due to their lower caloric content compared to regular sugars.
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Related Practice
Textbook Question
Name the epimers of D-glucose.
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Textbook Question
Identify the sugar in each description.
a. An aldopentose that is not D-arabinose forms D-arabinitol when it is reduced with NaBH4.
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Textbook Question
What is the configuration of each of the asymmetric centers in the Fischer projection of
a. D-glucose?
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Textbook Question
Identify the sugar in each description.
b. A sugar that is not D-altrose forms D-altraric acid when it is oxidized with nitric acid.
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Textbook Question
D-Xylose and D-lyxose are formed when d-threose undergoes a Kiliani–Fischer synthesis. D-Xylose is oxidized to an optically inactive aldaric acid, whereas D-lyxose forms an optically active aldaric acid. What are the structures of D-xylose and D-lyxose?
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