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 24
Which OH groups are in the axial position in each of the following?
a. β-D-idopyranose
b. α-D-allopyranose
Verified step by step guidance1
Step 1: Understand the structure of pyranose rings. Pyranose rings are six-membered cyclic structures formed by the reaction of an aldehyde or ketone group with a hydroxyl group in sugars. The axial and equatorial positions refer to the orientation of substituents on the ring relative to the plane of the ring.
Step 2: Analyze the chair conformation of b-D-idopyranose. In the beta configuration, the anomeric hydroxyl group (-OH) at the C1 position is equatorial. Identify the positions of other hydroxyl groups (C2, C3, C4, C5) and determine which are axial based on their orientation in the chair conformation.
Step 3: Analyze the chair conformation of a-D-allopyranose. In the alpha configuration, the anomeric hydroxyl group (-OH) at the C1 position is axial. Similarly, identify the positions of other hydroxyl groups (C2, C3, C4, C5) and determine which are axial based on their orientation in the chair conformation.
Step 4: Recall that axial positions alternate up and down around the ring in the chair conformation. Use the stereochemistry of each sugar to determine the specific orientation of each hydroxyl group. This requires knowledge of the sugar's Fischer projection and how it translates into the chair conformation.
Step 5: Summarize the axial hydroxyl groups for each sugar. For b-D-idopyranose, list the carbon positions where the hydroxyl groups are axial. For a-D-allopyranose, do the same. Ensure the stereochemistry is consistent with the given configurations (alpha or beta).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Axial and Equatorial Positions
In chair conformations of cyclohexane and related structures, substituents can occupy axial or equatorial positions. Axial substituents are oriented parallel to the axis of the ring, while equatorial substituents extend outward from the ring. This distinction affects steric interactions and stability, making it crucial for understanding the spatial arrangement of groups in cyclic compounds.
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Equatorial Preference
Pyranose Structure
Pyranose refers to a six-membered cyclic form of monosaccharides, derived from aldoses or ketoses. In pyranose, the anomeric carbon is typically involved in a glycosidic bond, influencing the orientation of hydroxyl (OH) groups. Understanding the structure of pyranoses is essential for determining the positions of substituents, such as OH groups, in the chair conformation.
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Anomeric Effect
The anomeric effect describes the preference for certain substituents at the anomeric carbon to adopt specific orientations due to electronic interactions. In pyranoses, this effect can influence whether OH groups are positioned axially or equatorially. Recognizing the anomeric effect is important for predicting the stability and reactivity of carbohydrate structures.
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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
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
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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