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
Draw the anomers of D-erythrofuranose.
Verified step by step guidance1
Understand the concept of anomers: Anomers are stereoisomers of cyclic sugars that differ in configuration only at the anomeric carbon (the carbon derived from the carbonyl group in the open-chain form). For D-erythrofuranose, this means we need to consider the two possible configurations (α and β) at the anomeric carbon.
Draw the open-chain form of D-erythrose: D-erythrose is an aldotetrose, meaning it has four carbons, with the first carbon being the aldehyde group. The second and third carbons are chiral, and the hydroxyl groups are arranged in the D-configuration (OH on the right in a Fischer projection).
Cyclize the molecule to form the furanose ring: D-erythrofuranose forms when the hydroxyl group on the third carbon (C3) attacks the aldehyde group on the first carbon (C1), creating a five-membered ring (furanose). This reaction forms a new chiral center at C1, the anomeric carbon.
Draw the two anomers: In the α-anomer, the hydroxyl group attached to the anomeric carbon (C1) is on the opposite side of the ring relative to the CH2OH group at C4 (down in a Haworth projection for D-sugars). In the β-anomer, the hydroxyl group at C1 is on the same side as the CH2OH group (up in a Haworth projection for D-sugars).
Label the structures: Clearly label the two structures as α-D-erythrofuranose and β-D-erythrofuranose to distinguish between the two anomers. Ensure the stereochemistry at all chiral centers is consistent with the D-configuration.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Anomers
Anomers are a specific type of stereoisomer found in carbohydrates, differing in configuration at the anomeric carbon, which is the carbon derived from the carbonyl group during cyclization. In the case of sugars, anomers can exist in two forms: alpha (α) and beta (β), depending on the orientation of the hydroxyl group attached to the anomeric carbon relative to the CH2OH group.
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Monosaccharides - Cyclization
D-erythrofuranose
D-erythrofuranose is a five-membered cyclic form of the sugar D-erythrose. It is a furanose, which means it contains a furan ring structure. Understanding its structure is crucial for identifying the anomers, as the anomeric carbon in D-erythrofuranose is the carbon that was originally the carbonyl carbon in the open-chain form of the sugar.
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Cyclization of Sugars
Cyclization is the process by which a linear sugar molecule forms a cyclic structure, typically through a reaction between a carbonyl group and a hydroxyl group. This process is fundamental in carbohydrate chemistry, as it leads to the formation of different anomeric forms and affects the sugar's reactivity and properties. Recognizing how cyclization occurs helps in drawing the correct anomers of D-erythrofuranose.
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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
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
4-Hydroxy- and 5-hydroxyaldehydes exist primarily as cyclic hemiacetals. Draw the structure of the cyclic hemiacetal formed by each of the following:
c. 5-hydroxypentanal
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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