Textbook Question
If α−galactose is dissolved in water, β−galactose is eventually present. Explain how this occurs.
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Ch.13 Carbohydrates
Timberlake13th EditionChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9780134421353
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Table of contents
- Ch.1 Chemistry in Our Lives11
- Ch.2 Chemistry and Measurements80
- Ch.3 Matter and Energy54
- Ch.4 Atoms and Elements51
- Ch.5 Nuclear Chemistry42
- Ch.6 Ionic and Molecular Compounds57
- Ch.7 Chemical Quantities and Reactions41
- Ch.8 Gases29
- Ch.9 Solutions51
- Ch.10 Acids and Bases and Equilibrium65
- Ch.11 Introduction to Organic Chemistry: Hydrocarbons78
- Ch.12 Alcohols, Thiols, Ethers, Aldehydes, and Ketones83
- Ch.13 Carbohydrates54
- Ch.14 Carboxylic Acids, Esters, Amines, and Amides90
- Ch.15 Lipids61
- Ch.16 Amino Acids, Proteins, and Enzymes84
- Ch.17 Nucleic Acids and Protein Synthesis83
- Ch.18 Metabolic Pathways and ATP Production67
Timberlake13th EditionChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9780134421353Not the one you use?Change textbook
Chapter 13, Problem 77b
Gentiobiose is found in saffron.
b. Is gentiobiose a reducing sugar? Explain.
Verified step by step guidance1
Step 1: Understand the definition of a reducing sugar. A reducing sugar is a carbohydrate that can act as a reducing agent because it has a free aldehyde group (-CHO) or a free ketone group (-C=O) in its structure. This is typically determined by the presence of a free anomeric carbon that is not involved in a glycosidic bond.
Step 2: Analyze the structure of gentiobiose. Gentiobiose is a disaccharide composed of two glucose molecules linked by a β(1→6) glycosidic bond. To determine if it is a reducing sugar, check if one of the glucose units has a free anomeric carbon.
Step 3: Identify the glycosidic bond in gentiobiose. The β(1→6) glycosidic bond connects the anomeric carbon of one glucose molecule to the hydroxyl group on the sixth carbon of the other glucose molecule. This means the anomeric carbon of one glucose is involved in the bond, but the other glucose molecule retains a free anomeric carbon.
Step 4: Determine if the free anomeric carbon can participate in redox reactions. Since one of the glucose units in gentiobiose has a free anomeric carbon, it can open up to form an aldehyde group, allowing it to act as a reducing sugar.
Step 5: Conclude that gentiobiose is a reducing sugar because it has a free anomeric carbon that can participate in redox reactions, fulfilling the criteria for a reducing sugar.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reducing Sugars
Reducing sugars are carbohydrates that can donate electrons to other molecules, typically due to the presence of a free aldehyde or ketone group. This property allows them to reduce certain chemical reagents, such as Benedict's or Fehling's solutions, which is a key characteristic in identifying these sugars. Common examples include glucose and fructose.
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Ketoses as Reducing Sugars Concept 2
Structure of Gentiobiose
Gentiobiose is a disaccharide composed of two glucose units linked by a glycosidic bond. Its structure includes a free anomeric carbon on one of the glucose units, which is crucial for determining its reducing properties. The presence of this free anomeric carbon allows gentiobiose to act as a reducing sugar.
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Chemical Tests for Reducing Sugars
Chemical tests, such as the Benedict's test, are used to identify reducing sugars by observing a color change when the sugar reduces copper(II) ions to copper(I) oxide. If gentiobiose is a reducing sugar, it will yield a positive result in these tests, indicating its ability to act as a reducing agent in solution.
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Related Practice
Textbook Question
α−Cellobiose is a disaccharide obtained from the hydrolysis of cellulose. It is quite similar to maltose except it has a β(1→4)−glycosidic bond. Draw the Haworth structure for α−cellobiose.
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Textbook Question
The disaccharide trehalose found in mushrooms is composed of two α-D-glucose molecules joined by an α(1→1)−glycosidic bond. Draw the Haworth structure for trehalose.
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