Textbook Question
Which configuration (R or S) does the bottom asymmetric carbon have for the D series of sugars? Which configuration for the L series?
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Ch. 23 - Carbohydrates and Nucleic Acids
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 23, Problem 6c,d
c. Draw d-idose, the C3 epimer of D-talose. Now compare your answers with Figure 23-3.
d. Draw the C4 “epimer” of D-xylose. Notice that this “epimer” is actually an L-series sugar, and we have seen its enantiomer. Give the correct name for this L-series sugar.
Verified step by step guidance1
Step 1: Understand the concept of epimers. Epimers are stereoisomers that differ in configuration at only one specific chiral center. For example, the C3 epimer of D-talose means that the configuration at the third carbon (C3) is inverted compared to D-talose.
Step 2: Draw the structure of D-talose. D-talose is an aldohexose (a six-carbon sugar with an aldehyde group at C1). Its stereochemistry at each chiral center (C2, C3, C4, and C5) follows the D-series convention. Refer to Figure 23-3 for the exact stereochemistry of D-talose.
Step 3: Modify the structure of D-talose to create D-idose, the C3 epimer. To do this, invert the stereochemistry at C3 while keeping the configurations at C2, C4, and C5 unchanged. Ensure the hydroxyl group (-OH) at C3 is flipped to the opposite side.
Step 4: For part d, draw the structure of D-xylose, which is an aldopentose (a five-carbon sugar with an aldehyde group at C1). Identify the stereochemistry at C2, C3, and C4 based on the D-series convention.
Step 5: Modify the structure of D-xylose to create the C4 'epimer.' Invert the stereochemistry at C4 while keeping the configurations at C2 and C3 unchanged. Notice that this inversion results in an L-series sugar. Compare the resulting structure to known sugars and identify its correct name as L-arabinose, the enantiomer of D-arabinose.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Epimers
Epimers are a specific type of diastereomer that differ in configuration at only one stereogenic center. In the context of sugars, epimers are important for understanding the structural variations between different monosaccharides. For example, d-idose and D-talose are epimers because they differ at one carbon atom, which affects their chemical properties and biological functions.
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Identifying Types of Stereoisomers
C3 and C4 Epimers
C3 and C4 epimers refer to the specific positions of the stereogenic centers that differ between two sugars. C3 epimers differ at the third carbon atom, while C4 epimers differ at the fourth carbon. This distinction is crucial for identifying and drawing the correct structures of sugars, as it influences their nomenclature and reactivity.
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L-series Sugars
L-series sugars are a classification of sugars based on their stereochemistry, specifically the configuration of the chiral carbon farthest from the aldehyde or ketone group. In the case of D-xylose, its C4 epimer is an L-series sugar, which means it has a different spatial arrangement at the fourth carbon. Understanding this classification helps in naming and distinguishing between enantiomers and their respective properties.
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Related Practice
Textbook Question
Talose is the C4 epimer of mannose. Draw the chair conformation of D-talopyranose.
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Textbook Question
Allose is the C3 epimer of glucose. Draw the cyclic hemiacetal form of D-allose, first in the chair conformation and then in the Haworth projection.
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Textbook Question
Draw the Haworth projection for the cyclic structure of D-mannose by laying down the Fischer projection.
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Textbook Question
a. Draw D-allose, the C3 epimer of glucose.
b. Draw D-talose, the C2 epimer of d-galactose
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Textbook Question
(a) There is only one ketotriose, called dihydroxyacetone. Draw its structure.
(b) There is only one aldotriose, called glyceraldehyde. Draw the two enantiomers of glyceraldehyde.
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