Textbook Question
D-Talose, a constituent of certain antibiotics, has the open-chain structure shown next. Draw d-talose in its cyclic hemiacetal form.
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 9b
Draw the structure that completes the mutarotation reaction between the two cyclic forms of (a) galactose and (b) fructose.
b. 
Verified step by step guidance1
Understand the concept of mutarotation: Mutarotation is the process by which the α and β anomers of a sugar interconvert in aqueous solution through the open-chain form. This occurs because the cyclic forms of sugars are in equilibrium with their linear form.
For galactose: Identify the two cyclic forms (α and β anomers) of galactose. These are pyranose forms (six-membered rings) where the difference lies in the orientation of the hydroxyl group (-OH) on the anomeric carbon (C1).
For galactose: Draw the open-chain form of galactose. This is the linear form of the sugar, which contains an aldehyde group at the top (C1) and hydroxyl groups attached to the other carbons.
For fructose: Identify the two cyclic forms (α and β anomers) of fructose. These are furanose forms (five-membered rings) where the difference lies in the orientation of the hydroxyl group (-OH) on the anomeric carbon (C2).
For fructose: Draw the open-chain form of fructose. This is the linear form of the sugar, which contains a ketone group at C2 and hydroxyl groups attached to the other carbons. The mutarotation reaction involves the interconversion between the cyclic and linear forms, allowing the α and β anomers to equilibrate.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Mutarotation
Mutarotation is the change in optical rotation that occurs when an anomeric carbon in a sugar ring opens and closes, interconverting between its alpha and beta forms. This process is significant in carbohydrates, as it affects the sugar's reactivity and properties. For example, in the case of galactose and fructose, the mutarotation involves the conversion of their cyclic forms into their respective open-chain forms and back to cyclic forms.
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Mutarotation Concept 1
Cyclic Forms of Sugars
Cyclic forms of sugars, also known as hemiacetals or hemiketals, are the structures that sugars adopt when they cyclize, typically involving the reaction of a carbonyl group with a hydroxyl group. For instance, galactose can exist in both alpha and beta forms, depending on the orientation of the hydroxyl group at the anomeric carbon. Understanding these structures is crucial for predicting the outcomes of reactions like mutarotation.
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Anomeric Carbon
The anomeric carbon is the carbon atom in a sugar that was originally part of the carbonyl group (aldehyde or ketone) and becomes a new chiral center upon cyclization. It plays a pivotal role in determining the alpha or beta configuration of the sugar. In the context of mutarotation, the anomeric carbon's configuration influences the sugar's reactivity and interactions with other molecules, making it essential for understanding the reaction mechanisms.
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Related Practice
Textbook Question
The cyclic structure of D-idose, an aldohexose, is shown in the margin. Convert this to the straight-chain Fischer projection structure.
Textbook Question
Draw the structure that completes the mutarotation reaction between the two cyclic forms of (a) galactose and (b) fructose.
a.
Textbook Question
In the monosaccharide hemiacetal shown below number all the carbon atoms, identify the anomeric carbon atom, and identify it as the α or β anomer.
Textbook Question
L-Fucose is one of the naturally occurring L monosaccharides. It is present in the short chains of monosaccharides by which blood groups are classified. Compare the structure of L-fucose shown in the margin with the structures of α- and β-D-galactose and answer the following questions.
d. "Fucose” is a common name. Is 6-deoxy-L-galactose a correct name for fucose? Why or why not?
Textbook Question
Draw the structure of the α and β anomers that result from the reaction of methanol and ribose. Are these compounds acetals or hemiacetals?