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 26
Why is only a trace amount of acid used in the formation of an N-glycoside?
Verified step by step guidance1
Understand the context: The formation of an N-glycoside involves the reaction of a sugar (typically in its cyclic hemiacetal form) with an amine. This reaction is acid-catalyzed, meaning a small amount of acid is used to facilitate the process.
Recognize the role of the acid: The acid protonates the hydroxyl group of the sugar, making it a better leaving group. This step is crucial for the formation of the oxocarbenium ion intermediate, which is highly reactive and facilitates the nucleophilic attack by the amine.
Consider the sensitivity of the reactants: Sugars are prone to degradation under strongly acidic conditions, such as hydrolysis or dehydration reactions. Using only a trace amount of acid minimizes the risk of side reactions and ensures the sugar remains intact during the reaction.
Acknowledge the catalytic nature of the acid: Since the acid is not consumed in the reaction, only a catalytic (trace) amount is needed to continuously facilitate the formation of the oxocarbenium ion and drive the reaction forward.
Conclude the reasoning: Using a trace amount of acid ensures that the reaction proceeds efficiently while avoiding excessive degradation of the sugar or other unwanted side reactions, leading to the selective formation of the N-glycoside.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
N-glycoside Formation
N-glycosides are formed when a sugar molecule reacts with an amine, resulting in a glycosidic bond. This reaction typically requires an acid catalyst to activate the sugar, making it more electrophilic and facilitating the nucleophilic attack by the amine. Understanding this process is crucial for grasping why specific conditions, such as the use of trace amounts of acid, are employed.
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General Reaction
Acid Catalysis
Acid catalysis involves the use of an acid to increase the rate of a chemical reaction. In the context of N-glycoside formation, a small amount of acid is sufficient to protonate the sugar, enhancing its reactivity without overwhelming the reaction. Excess acid can lead to side reactions or degradation of the sugar, making controlled use essential.
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Selectivity in Organic Reactions
Selectivity refers to the preference of a reaction to produce a particular product over others. In the formation of N-glycosides, using only a trace amount of acid helps ensure that the desired glycosidic bond forms preferentially, minimizing by-products. This selectivity is vital for achieving high yields and purity in organic synthesis.
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Related Practice
Textbook Question
Name the following compounds and indicate whether or not each is a reducing sugar:
b.
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Textbook Question
Name the following compounds and indicate whether or not each is a reducing sugar:
a.
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Textbook Question
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?
Textbook Question
Name the following compounds and indicate whether or not each is a reducing sugar:
c.
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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