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 39b
What is the configuration of each of the asymmetric centers in the Fischer projection of
b. D-galactose?
Verified step by step guidance1
Step 1: Understand the Fischer projection of D-galactose. D-galactose is a monosaccharide with the molecular formula C6H12O6. It has four asymmetric centers (chiral carbons) in its Fischer projection.
Step 2: Identify the configuration of each chiral center. In a Fischer projection, horizontal lines represent bonds projecting out of the plane (towards the viewer), and vertical lines represent bonds projecting into the plane (away from the viewer). The configuration of each chiral center is determined by the arrangement of the substituents around the carbon atom.
Step 3: Assign priorities to the substituents on each chiral center using the Cahn-Ingold-Prelog (CIP) priority rules. The substituents are ranked based on atomic number, and the configuration is determined by the order in which the substituents are arranged.
Step 4: Determine the absolute configuration (R or S) of each chiral center. To do this, visualize the molecule in 3D and trace the path from the highest priority substituent to the lowest priority substituent. If the path is clockwise, the configuration is R; if counterclockwise, it is S.
Step 5: Verify the D-configuration of D-galactose. The D-configuration is determined by the orientation of the hydroxyl group (-OH) on the penultimate carbon (second-to-last carbon). In D-galactose, the hydroxyl group on the penultimate carbon is on the right side in 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). Each asymmetric center in a molecule can have two configurations, typically designated as 'R' (rectus) or 'S' (sinister), based on the Cahn-Ingold-Prelog priority rules. Understanding chirality is crucial for determining the optical activity and biological interactions of molecules.
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D and L Notation
The D and L notation is used to classify sugars based on the configuration of their asymmetric carbon furthest from the aldehyde or ketone group. In D-sugars, the hydroxyl group (-OH) on this carbon is on the right in a Fischer projection, while in L-sugars, it is on the left. This notation is essential for distinguishing between different stereoisomers of carbohydrates, which can have vastly different biological functions.
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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?
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Textbook Question
What is the configuration of each of the asymmetric centers in the Fischer projection of
e. D-sorbose?
1
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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
What is the configuration of each of the asymmetric centers in the Fischer projection of
d. D-xylose?
1
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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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