Textbook Question
Answer the following questions about the eight aldopentoses:
a. Which are enantiomers?
b. Which are C-2 epimers?
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 39a
What is the configuration of each of the asymmetric centers in the Fischer projection of
a. D-glucose?
Verified step by step guidance1
Step 1: Understand the Fischer projection. In a Fischer projection, the horizontal lines represent bonds projecting out of the plane (toward the viewer), and the vertical lines represent bonds projecting into the plane (away from the viewer). Each intersection represents a carbon atom, and asymmetric centers are carbons bonded to four different groups.
Step 2: Identify the asymmetric centers in d-glucose. In the Fischer projection of d-glucose, the asymmetric centers are the carbon atoms that are bonded to four distinct groups. These are typically the carbons in the backbone of the molecule, excluding the aldehyde group (CHO) and the terminal CH2OH group.
Step 3: Assign priorities to the substituents on each asymmetric center using the Cahn-Ingold-Prelog (CIP) priority rules. The substituents are ranked based on atomic number, and ties are broken by looking at the atoms directly bonded to the substituents.
Step 4: Determine the configuration (R or S) of each asymmetric center. To do this, visualize the molecule in 3D or use the Fischer projection directly. Assign the configuration based on the arrangement of the substituents, ensuring that the lowest priority group is pointing away from the viewer.
Step 5: Repeat the process for each asymmetric center in d-glucose. Carefully analyze each carbon atom to determine its configuration, ensuring that you follow the CIP rules and correctly interpret the Fischer projection.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Fischer Projections
Fischer projections are a two-dimensional representation of three-dimensional organic molecules, particularly carbohydrates. In these projections, vertical lines represent bonds that extend away from the viewer, while horizontal lines indicate bonds that come towards the viewer. This format is particularly useful for visualizing the stereochemistry of molecules, especially those with multiple chiral centers.
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Monosaccharides - Drawing Fischer Projections
Chirality and Asymmetric Centers
Chirality refers to the property of a molecule that makes it non-superimposable on its mirror image, often due to the presence of asymmetric centers (chiral centers). An asymmetric center is typically a carbon atom bonded to four different substituents, leading to two possible configurations (R or S). Understanding chirality is crucial for determining the optical activity and biological function of sugars like d-glucose and d-talose.
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D and L Configuration
The D and L notation is used to classify sugars based on the orientation of the hydroxyl group (-OH) on the penultimate carbon (the second-to-last carbon) in the Fischer projection. If the -OH group is on the right side, the sugar is designated as D; if it is on the left, it is designated as L. This classification is essential for distinguishing between different stereoisomers of sugars, which can have vastly different 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
b. D-galactose?
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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
d. D-xylose?
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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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