Textbook Question
Without referring to the chapter, draw the chair conformations of
(d) N-acetylglucosamine, glucose with the C2 oxygen atom replaced by an acetylated amino group.
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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 48a,b,c
Use Figure 23-3 (the D family of aldoses) to name the following aldoses.
(a) the C2 epimer of D-arabinose
(b) the C3 epimer of D-mannose
(c) the C3 epimer of D-threose
Verified step by step guidance1
Step 1: Understand the concept of epimers. Epimers are stereoisomers that differ in configuration at only one specific carbon atom, while the rest of the molecule remains identical. For aldoses, this means identifying the carbon atom where the configuration changes.
Step 2: For part (a), identify the C2 epimer of D-arabinose. Locate D-arabinose in Figure 23-3 (the D family of aldoses). D-arabinose is a five-carbon aldose (aldopentose). To find its C2 epimer, invert the stereochemistry at the second carbon (C2) while keeping the rest of the molecule unchanged.
Step 3: For part (b), identify the C3 epimer of D-mannose. Locate D-mannose in Figure 23-3. D-mannose is a six-carbon aldose (aldohexose). To find its C3 epimer, invert the stereochemistry at the third carbon (C3) while keeping the rest of the molecule unchanged.
Step 4: For part (c), identify the C3 epimer of D-threose. Locate D-threose in Figure 23-3. D-threose is a four-carbon aldose (aldotetrose). To find its C3 epimer, invert the stereochemistry at the third carbon (C3) while keeping the rest of the molecule unchanged.
Step 5: After identifying the epimers for each part, use the names provided in Figure 23-3 to assign the correct name to each epimer. Ensure that the D-configuration is maintained for all the aldoses.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aldoses
Aldoses are a type of monosaccharide characterized by the presence of an aldehyde group (-CHO) at one end of the molecule. They can vary in the number of carbon atoms, and their structure influences their reactivity and biological function. Understanding aldoses is crucial for identifying their epimers, which are stereoisomers differing at one specific carbon atom.
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General Reaction
Epimers
Epimers are a specific type of diastereomer that differ in configuration at only one stereogenic center. In the context of aldoses, identifying epimers involves recognizing how the orientation of hydroxyl (-OH) groups changes at specific carbon atoms. This concept is essential for naming aldoses based on their structural variations, such as the C2 or C3 epimers mentioned in the question.
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D and L Configuration
The D and L configuration refers to the stereochemical designation of sugars based on the orientation of the hydroxyl group on the chiral carbon farthest from the aldehyde group. D-sugars have the hydroxyl group on the right in a Fischer projection, while L-sugars have it on the left. This classification is fundamental for naming aldoses and understanding their relationships, including the identification of epimers.
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Related Practice
Textbook Question
Without referring to the chapter, draw the chair conformations of
(b) α-D-allopyranose (the C3 epimer of glucose).
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Textbook Question
Without referring to the chapter, draw the chair conformations of
(c) β-D-galactopyranose (the C4 epimer of glucose).
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Textbook Question
Classify the following monosaccharides. (Examples: D-aldohexose, L-ketotetrose.)
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Textbook Question
(a) Give the products expected when (+)-glyceraldehyde reacts with HCN.
(b) What is the relationship between the products? How might they be separated?
(c) Are the products optically active? Explain.
Textbook Question
The relative configurations of the stereoisomers of tartaric acid were established by the following syntheses:
(1) D-(+)-glyceraldehyde diastereomers A and B (separated)
(2) Hydrolysis of A and B using aqueous Ba(OH)2 gave C and D, respectively.
(3) HNO3 oxidation of C and D gave (-)-tartaric acid and meso-tartaric acid, respectively.
(a) You know the absolute configuration of D-(+)-glyceraldehyde. Use Fischer projections to show the absolute configurations of products A, B, C, and D.
(b) Show the absolute configurations of the three stereoisomers of tartaric acid: (+)-tartaric acid, (-)-tartaric acid, and meso-tartaric acid.
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