Textbook Question
Name four important monosaccharides and tell where each occurs in nature.
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Ch.20 Carbohydrates
McMurry8th EditionFundamentals of GOBISBN: 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
Chapter 20, Problem 42b
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”?
Verified step by step guidance1
Understand the concept of optical rotation: Optical rotation refers to the ability of a compound to rotate plane-polarized light. Compounds that rotate light to the right are called dextrorotatory (denoted as '+'), while those that rotate light to the left are called levorotatory (denoted as '-').
Recognize the behavior of sucrose: Sucrose is dextrorotatory, meaning it rotates plane-polarized light to the right. This is due to the combined optical activities of its glucose and fructose components in the intact molecule.
Analyze the hydrolysis of sucrose: During hydrolysis, sucrose breaks down into its monosaccharide components, d-glucose and d-fructose. While d-glucose is dextrorotatory, d-fructose is strongly levorotatory. The levorotatory effect of d-fructose dominates in the mixture.
Explain the term 'invert sugar': After hydrolysis, the overall optical rotation of the mixture changes direction from right (dextrorotatory) to left (levorotatory). This inversion of the direction of rotation is why the resulting mixture is called 'invert sugar.'
Summarize the significance: The term 'invert sugar' reflects the change in optical rotation caused by the hydrolysis of sucrose into its monosaccharide components, which alters the net optical activity of the solution.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Optical Activity
Optical activity refers to the ability of certain substances to rotate plane-polarized light. This property is due to the chiral nature of the molecules, which can exist in two enantiomeric forms that interact differently with light. For example, d-glucose and sucrose rotate light to the right (dextrorotatory), while d-fructose rotates it to the left (levorotatory).
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Hydrolysis of Sucrose
Hydrolysis of sucrose involves breaking down the disaccharide into its constituent monosaccharides, glucose and fructose, typically through the action of an enzyme or acid. This reaction alters the optical activity of the solution, as the resulting mixture of glucose and fructose exhibits a net rotation to the left, contrasting with the right rotation of sucrose.
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Invert Sugar
Invert sugar is the term used for the mixture of glucose and fructose produced when sucrose is hydrolyzed. The name 'invert' comes from the fact that the hydrolysis process changes the direction of optical rotation from right to left, indicating a change in the sugar's properties. Invert sugar is sweeter than sucrose and is commonly used in food products for its desirable taste and moisture-retaining qualities.
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Related Practice
Textbook Question
Only three stereoisomers are possible for 2,3-dibromo-2, 3-dichlorobutane. Draw them, indicating which pair are enantiomers (optical isomers). Why does the other isomer not have an enantiomer?
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Textbook Question
In Section 15.6, you saw that aldehydes react with reducing agents to yield primary alcohols (RCH=O → RCH2OH). The structures of two D-aldotetroses are shown. One of them can be reduced to yield a chiral product, but the other yields an achiral product. Explain.
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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.
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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.
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Textbook Question
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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