Textbook Question
Identify the following carbohydrates as the ⍺ or β anomer:
(b)
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Ch.6 Carbohydrates Life's Sweet Molecules
Frost4th EditionGeneral, Organic and Biological ChemistryISBN: 9780134988696
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Table of contents
- Ch.4 Introduction to Organic Compounds75
- Ch.5 Chemical Reactions19
- Ch.6 Carbohydrates Life's Sweet Molecules62
- Ch.7 States of Matter and Their Attractive Forces8
- Ch.8 Solution Chemistry Sugar and Water Do Mix4
- Ch.10 Proteins Workers of the Cell89
- Ch.11 Nucleic Acids Big Molecules with a Big Role69
- Ch.12 Food as Fuel An Overview of Metabolism65
Frost4th EditionGeneral, Organic and Biological ChemistryISBN: 9780134988696Not the one you use?Change textbook
Chapter 3, Problem 75a
Will the following carbohydrates produce a positive Benedict's test?
a. D-glucose
Verified step by step guidance1
Understand the Benedict's test: The Benedict's test is used to identify reducing sugars. Reducing sugars are carbohydrates that have a free aldehyde group (-CHO) or a free ketone group that can be oxidized. When a reducing sugar is present, the Benedict's reagent (containing Cu2+) reacts with the sugar, producing a red-orange precipitate of Cu2O.
Identify the structure of d-glucose: d-glucose is a monosaccharide with an aldehyde functional group in its open-chain form. This aldehyde group makes d-glucose a reducing sugar.
Determine if d-glucose can undergo oxidation: Since d-glucose has a free aldehyde group, it can be oxidized by the Cu2+ ions in Benedict's reagent, resulting in a positive test.
Relate the result to the Benedict's test: Because d-glucose is a reducing sugar, it will produce a positive Benedict's test, forming a red-orange precipitate.
Conclude the reasoning: Based on the chemical properties of d-glucose and its ability to act as a reducing sugar, it will indeed produce a positive Benedict's test.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Benedict's Test
Benedict's test is a qualitative assay used to detect reducing sugars, which can donate electrons to other molecules. When a reducing sugar is present, the copper(II) ions in the Benedict's reagent are reduced to copper(I) oxide, resulting in a color change that ranges from green to brick red, depending on the concentration of the sugar.
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Reducing Sugars
Reducing sugars are carbohydrates that have a free aldehyde or ketone group capable of acting as a reducing agent. Common examples include monosaccharides like glucose and fructose, as well as some disaccharides like maltose. These sugars can participate in redox reactions, making them detectable by tests like Benedict's.
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D-Glucose
D-glucose is a simple sugar and a primary energy source for cells. It is a six-carbon aldose that readily participates in reducing reactions due to its free aldehyde group. As a reducing sugar, d-glucose will yield a positive result in a Benedict's test, indicating its presence in a solution.
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Related Practice
Textbook Question
Draw the Fischer projection of the product of the oxidation of D-galactose at C1.
750
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Textbook Question
Draw the Fischer projection of the product of reduction reaction of D-galactose at C1.
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Textbook Question
Will the following carbohydrates produce a positive Benedict’s test?
b. lactose
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Textbook Question
Draw the product of the following 1→4 condensation and name the glycosidic bond:
668
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Textbook Question
Isomaltose, a disaccharide formed during caramelization in cooking, contains two glucose units bonded ⍺(1→6). Draw the structure of isomaltose.
906
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