Textbook Question
Consider the trisaccharide A, B, C shown in Problem 20.23.
a. Identify the hemiacetal and acetal linkages.
Ch.20 Carbohydrates
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook
Chapter 20, Problem 21
Identify the following as diastereomers, enantiomers, and/or anomers.
(a) β-D-fructose and β-D-fructose
(b) D-galactose and L-galactose
(c) L-allose and D-glucose (both aldohexoses)
Verified step by step guidance1
Step 1: Understand the definitions of the terms. Diastereomers are stereoisomers that are not mirror images of each other. Enantiomers are stereoisomers that are non-superimposable mirror images. Anomers are a specific type of diastereomer that differ in configuration at the anomeric carbon (the carbon derived from the carbonyl group in a sugar).
Step 2: Analyze part (a). Compare ß-d-fructose and ß-d-fructose. Since they are the same molecule, they are neither diastereomers, enantiomers, nor anomers. They are identical.
Step 3: Analyze part (b). Compare d-galactose and l-galactose. These are mirror images of each other and are non-superimposable. Therefore, they are enantiomers.
Step 4: Analyze part (c). Compare l-allose and d-glucose. Both are aldohexoses, but they differ in the arrangement of groups at multiple chiral centers. Since they are not mirror images, they are diastereomers.
Step 5: Summarize the findings. (a) Identical molecules, not diastereomers, enantiomers, or anomers. (b) Enantiomers. (c) Diastereomers.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Diastereomers
Diastereomers are stereoisomers that are not mirror images of each other. They occur when two or more stereocenters are present in a molecule, leading to different spatial arrangements of atoms. Unlike enantiomers, which have identical physical properties except for their interaction with polarized light, diastereomers can have significantly different chemical and physical properties.
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Enantiomers vs Diastereomers Concept 1
Enantiomers
Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. Each enantiomer has at least one chiral center, and they often exhibit different optical activities, meaning they rotate plane-polarized light in opposite directions. Enantiomers can have vastly different biological activities, making their distinction crucial in fields like pharmacology.
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Anomers
Anomers are a specific type of stereoisomer that differ at the anomeric carbon, which is the carbon atom that becomes a new chiral center when a sugar cyclizes. In the case of carbohydrates, anomers are typically designated as alpha (α) or beta (β) based on the orientation of the hydroxyl group at the anomeric carbon. This distinction is important in understanding the reactivity and properties of sugars in biological systems.
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Related Practice
Textbook Question
Draw the structure of the α and β anomers that result from the reaction of methanol and ribose. Are these compounds acetals or hemiacetals?
Textbook Question
Hydrolysis of both glycosidic bonds in the following trisaccharide A, B, C yields three monosaccharides.
c. Draw the Fischer projections for the three monosaccharides.
Textbook Question
How would you classify the link between the monosaccharides in cellobiose?
Textbook Question
During the digestion of starch from potatoes, the enzyme α-amylase catalyzes the hydrolysis of starch into maltose. Subsequently, the enzyme maltase catalyzes the hydrolysis of maltose into two glucose units. Write an equation (in words) for the enzymatic conversion of starch to glucose. Classify each of the carbohydrates in the equation as a disaccharide, monosaccharide, or polysaccharide.
Textbook Question
Consider the trisaccharide A, B, C shown in Problem 20.23.
c. State the numbers of the carbon atoms that form glycosidic linkages between monosaccharide A and monosaccharide B.