Textbook Question
What is the configuration of each of the asymmetric centers in the Fischer projection of
b. D-galactose?
3
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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 38a,b
Answer the following questions about the eight aldopentoses:
a. Which are enantiomers?
b. Which are C-2 epimers?
Verified step by step guidance1
Step 1: Understand the structure of aldopentoses. Aldopentoses are monosaccharides with five carbon atoms, including an aldehyde group at the C-1 position. The remaining carbons have hydroxyl groups attached, and the stereochemistry at the chiral centers determines the specific aldopentose.
Step 2: Define enantiomers. Enantiomers are pairs of molecules that are non-superimposable mirror images of each other. For aldopentoses, enantiomers will have opposite configurations at all chiral centers.
Step 3: Identify the eight aldopentoses. The eight aldopentoses include D-ribose, D-arabinose, D-xylose, D-lyxose, and their corresponding L-forms (L-ribose, L-arabinose, L-xylose, L-lyxose). Enantiomers are formed by pairing each D-form with its corresponding L-form.
Step 4: Define epimers. Epimers are stereoisomers that differ in configuration at only one chiral center. For C-2 epimers, the difference occurs specifically at the second carbon atom. Compare the stereochemistry at C-2 for each aldopentose to identify pairs that differ only at this position.
Step 5: Analyze the aldopentoses to determine C-2 epimers. For example, D-ribose and D-arabinose differ only at the C-2 position, making them C-2 epimers. Similarly, L-ribose and L-arabinose are C-2 epimers. Repeat this analysis for other pairs of aldopentoses to identify additional C-2 epimers.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aldopentoses
Aldopentoses are a class of monosaccharides that contain five carbon atoms and an aldehyde functional group. They are important in biochemistry and can exist in various stereoisomeric forms. The eight aldopentoses include ribose, arabinose, xylose, and lyxose, each differing in the arrangement of hydroxyl groups around the carbon skeleton.
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Enantiomers
Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. They typically arise in molecules that have one or more chiral centers, leading to two distinct configurations. In the context of aldopentoses, identifying enantiomers involves recognizing pairs of sugars that differ at all chiral centers.
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Epimers
Epimers are a specific type of diastereomer that differ in configuration at only one chiral center. In aldopentoses, C-2 epimers refer to sugars that have different configurations at the second carbon atom while remaining identical at all other chiral centers. Understanding epimerism is crucial for distinguishing between closely related sugars and their biological roles.
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Related Practice
Textbook Question
What is the configuration of each of the asymmetric centers in the Fischer projection of
c. D-ribose?
2
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Textbook Question
Identify the sugar in each description.
c. A ketose that, when reduced with NaBH4, forms D-altritol and D-allitol.
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Textbook Question
What is the configuration of each of the asymmetric centers in the Fischer projection of
a. D-glucose?
1
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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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