Textbook Question
Look at the open-chain form of D-mannose and draw the two glycosidic products that you expect to obtain by reacting D-mannose with methanol.
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 53
Reduction of D-fructose with a reducing agent yields a mixture of D-sorbitol along with a second, isomeric product. What is the structure of the second product?
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Understand the context: Reduction of D-fructose involves the addition of hydrogen (H₂) to the carbonyl group (C=O) in the sugar molecule, converting it into an alcohol group (-OH). This process is typically carried out using a reducing agent such as sodium borohydride (NaBH₄) or hydrogen gas with a catalyst.
Identify the structure of D-fructose: D-fructose is a ketohexose, meaning it contains six carbons and a ketone group at the second carbon (C2). The ketone group is the functional group that will be reduced.
Determine the products of reduction: Reduction of the ketone group in D-fructose can yield two different products because the ketone group is located at C2, which is adjacent to a chiral center (C3). Reduction can produce either D-sorbitol (a sugar alcohol derived from D-glucose) or another isomeric sugar alcohol.
Explain the formation of the second product: The second product is D-mannitol, which forms when the reduction of the ketone group leads to the formation of a hydroxyl group (-OH) with the opposite stereochemistry at C2 compared to D-sorbitol. This occurs because the reduction process can produce a racemic mixture at the C2 position.
Summarize the structures: The two products of the reduction of D-fructose are D-sorbitol (with the same stereochemistry as D-glucose) and D-mannitol (with the stereochemistry of D-mannose). Both are sugar alcohols, differing only in the configuration of the hydroxyl group at C2.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reduction of Sugars
Reduction of sugars involves the conversion of carbonyl groups (aldehydes or ketones) into alcohols using reducing agents. In the case of d-fructose, a ketose sugar, reduction leads to the formation of d-sorbitol, an alditol. Understanding this process is crucial for predicting the products of sugar reduction.
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Isomerism
Isomerism refers to the existence of compounds with the same molecular formula but different structural arrangements or spatial orientations. In the context of d-fructose reduction, the second product formed alongside d-sorbitol is likely to be an isomer, such as d-mannitol, which has a different configuration at one or more carbon atoms.
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Structural Representation of Sugars
Structural representation of sugars involves depicting their molecular structure, including the arrangement of atoms and functional groups. For d-fructose and its reduction products, understanding how to draw and interpret Fischer projections or Haworth structures is essential for identifying the second product's structure and its relationship to d-sorbitol.
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Related Practice
Textbook Question
Oxidation of the aldehyde group of ribose yields a carboxylic acid. Draw the structure of ribonic acid.
Textbook Question
In its open-chain form, D-mannose, an aldohexose found in orange peels, has the structure shown here. Coil mannose around and draw it in the cyclic hemiacetal ⍺ and β forms.
Textbook Question
Treatment of D-glucose with a reducing agent yields sorbitol, a substance used as a sugar substitute by people with diabetes. Draw the structure of sorbitol.
Textbook Question
Treatment of an aldose with an oxidizing agent such as Tollens’ reagent yields a carboxylic acid. Gluconic acid, the product of glucose oxidation, is used as its magnesium salt for the treatment of magnesium deficiency. Draw the structure of gluconic acid.
Textbook Question
Sucrose and D-glucose rotate plane-polarized light to the right; D-fructose rotates light to the left. When sucrose is hydrolyzed, the glucose–fructose mixture rotates light to the left.
b. Why do you think the mixture is called “invert sugar”?