Textbook Question
Draw the products formed when β-D-galactose reacts with ethanol and HCl. (Show all structures as chair conformers.)
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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 22-23
When glucose undergoes base-catalyzed isomerization in the absence of the enzyme, mannose is one
of the products that is formed (Section 20.5). Why is mannose not formed in the enzyme-catalyzed reaction?
Verified step by step guidance1
Understand the process of base-catalyzed isomerization: In a base-catalyzed isomerization, glucose can undergo an enediol rearrangement, which allows it to convert into different isomers, such as mannose.
Recognize the role of enzymes in isomerization: Enzymes are highly specific catalysts that facilitate reactions by lowering the activation energy and stabilizing transition states. They often have specific active sites that only allow certain substrates to bind.
Identify the specificity of the enzyme involved: In the enzyme-catalyzed isomerization of glucose, the enzyme is specific to the conversion of glucose to fructose, not mannose. This specificity is due to the enzyme's active site, which is tailored to facilitate the conversion to fructose.
Consider the structural differences: Mannose and fructose have different structural arrangements. The enzyme's active site is designed to accommodate the transition state leading to fructose, not mannose.
Conclude why mannose is not formed: Due to the enzyme's specificity and the structural requirements of its active site, mannose is not formed in the enzyme-catalyzed reaction, as the enzyme does not facilitate the necessary rearrangement for mannose formation.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Base-Catalyzed Isomerization
Base-catalyzed isomerization involves the rearrangement of molecular structures through the action of a base, which facilitates the conversion of one isomer to another. In the case of glucose, the base can deprotonate hydroxyl groups, allowing for the formation of different structural isomers, such as mannose. This reaction typically occurs under non-enzymatic conditions, leading to a mixture of products.
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Base Catalyzed
Enzyme Specificity
Enzymes are biological catalysts that accelerate chemical reactions with high specificity for their substrates. In the case of glucose isomerization, enzymes like glucose isomerase preferentially convert glucose to fructose rather than mannose. This specificity arises from the enzyme's active site, which is shaped to fit certain substrates, thus preventing the formation of alternative products like mannose.
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Reaction Mechanism
The reaction mechanism describes the step-by-step process by which reactants are converted into products. In enzyme-catalyzed reactions, the mechanism often involves multiple intermediates and specific transition states that are stabilized by the enzyme. Understanding the mechanism of glucose isomerization helps explain why mannose is not produced when the reaction is catalyzed by an enzyme, as the pathway diverges from that leading to mannose.
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Related Practice
Textbook Question
D-Glucose most often exists as a pyranose, but it can also exist as a furanose. Draw the Haworth projection of α-D-glucofuranose
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Textbook Question
Why is only a trace amount of acid used in the formation of an N-glycoside?
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Textbook Question
Draw the anomers of D-erythrofuranose.
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Textbook Question
4-Hydroxy- and 5-hydroxyaldehydes exist primarily as cyclic hemiacetals. Draw the structure of the cyclic hemiacetal formed by each of the following:
d. 4-hydroxyheptanal
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Textbook Question
Which OH groups are in the axial position in each of the following?
a. β-D-idopyranose
b. α-D-allopyranose
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