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 47a
Without referring to the chapter, draw the chair conformations of
(a) β-D-mannopyranose (the C2 epimer of glucose).
Verified step by step guidance1
Understand the structure of β-D-mannopyranose: It is the C2 epimer of β-D-glucopyranose, meaning the hydroxyl group (-OH) on carbon 2 (C2) is oriented differently compared to β-D-glucopyranose. In β-D-mannopyranose, the -OH group on C2 is axial (pointing down in the chair conformation), while in β-D-glucopyranose, it is equatorial (pointing outwards).
Draw the basic pyranose ring in the chair conformation: Start by sketching a six-membered ring in the chair form, which is the most stable conformation for pyranose sugars. Label the carbons from C1 to C6 in a clockwise direction, starting with the anomeric carbon (C1).
Place the substituents on the ring: For β-D-mannopyranose, the anomeric hydroxyl group (-OH) on C1 is equatorial (pointing outwards), as it is in the β-anomer. The hydroxyl group on C2 is axial (pointing down), and the remaining hydroxyl groups on C3, C4, and C6 are equatorial. The -CH2OH group on C5 is also equatorial.
Verify the stereochemistry: Double-check the orientation of each substituent to ensure it matches the β-D-mannopyranose structure. Remember that the axial and equatorial positions alternate around the ring, and the stereochemistry of each carbon is determined by the sugar's configuration.
Draw the final chair conformation: Clearly depict the chair conformation of β-D-mannopyranose with all substituents in their correct positions. Highlight the axial -OH group on C2 to emphasize the difference from β-D-glucopyranose.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Chair Conformation
Chair conformation is a three-dimensional representation of cyclohexane and its derivatives, which minimizes steric strain and torsional strain. In this conformation, the carbon atoms are arranged in a staggered manner, allowing for more stable interactions between substituents. Understanding chair conformations is crucial for analyzing the spatial arrangement of atoms in cyclic sugars like mannopyranose.
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Understanding what a conformer is.
Pyranose Structure
Pyranose refers to a six-membered ring structure formed by the cyclization of monosaccharides, specifically aldoses and ketoses. In the case of D-mannopyranose, the ring consists of five carbon atoms and one oxygen atom. Recognizing the pyranose structure is essential for understanding the chemical properties and reactivity of sugars, as well as their conformational variations.
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Epimerization
Epimerization is the process by which two sugars differ in configuration at only one specific carbon atom. In the context of D-mannopyranose, it is the C2 epimer of glucose, meaning they differ in the orientation of the hydroxyl group at the second carbon. This concept is important for distinguishing between different sugars and understanding their biological roles and interactions.
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Related Practice
Textbook Question
Ribonucleosides are not so easily hydrolyzed, requiring relatively strong acid. Using your mechanism for part (a), show why cytidine and adenosine (for example) are not so readily hydrolyzed. Explain why this stability is important for living organisms.
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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
Glucose is the most abundant monosaccharide. From memory, draw glucose in
(a) the Fischer projection of the open chain.
(b) the most stable chair conformation of the most stable pyranose anomer.
(c) the Haworth projection of the most stable pyranose anomer.
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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
All of the rings of the four heterocyclic bases are aromatic. This is more apparent when the polar resonance forms of the amide groups are drawn, as is done for thymine here. Redraw the hydrogen-bonded guanine-cytosine and adenine-thymine pairs shown in Figure 23-24, using the polar resonance forms of the amides. Show how these forms help to explain why the hydrogen bonds involved in these pairings are particularly strong. Remember that a hydrogen bond arises between an electron-deficient hydrogen atom and an electron-rich pair of nonbonding electrons.
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