Textbook Question
Starting with a Fischer projection of d-glucose (and other sugars), switch only the stereocenter that gave it the designation of d. What new sugar have you made? [Hint: The answer is not l-glucose.]
Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 26, Problem 70
The α- and β-anomers of glucose are shown here.
In solution, these two epimers can interconvert through a process called mutarotation. What is the ratio of anomers (α:β) when the specific rotation is +52.6°
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, leading to an equilibrium mixture. Each anomer has a specific optical rotation, and the observed rotation of the solution is the weighted average of the rotations of the two anomers based on their proportions.
Identify the specific rotations of the α- and β-anomers of glucose: The specific rotation of the α-anomer of glucose is +112.2°, and the specific rotation of the β-anomer of glucose is +18.7°. These values are typically provided or can be found in reference materials.
Set up the equation for the observed specific rotation: The observed specific rotation of the solution (+52.6°) is the weighted average of the specific rotations of the two anomers. Use the equation: , where x and y are the proportions of the α- and β-anomers, respectively.
Express the relationship between the proportions: Since the total proportion of the two anomers must equal 1, you can write: . Solve for one variable in terms of the other (e.g., ).
Substitute the proportions into the weighted average equation: Use the equation for the observed specific rotation: . Substitute into the equation and solve for x (proportion of α-anomer). Once x is determined, calculate y (proportion of β-anomer). Finally, express the ratio α:β as x:y.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Anomers
Anomers are a type of stereoisomer found in carbohydrates, specifically cyclic forms of sugars. They differ in configuration at the anomeric carbon, which is the carbon derived from the carbonyl carbon during the formation of the cyclic structure. In glucose, the α-anomer has the hydroxyl group on the anomeric carbon pointing down, while the β-anomer has it pointing up.
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12:58
Monosaccharides - Cyclization
Mutarotation
Mutarotation is the process by which the α and β anomers of a sugar interconvert in solution. This occurs through the opening of the cyclic form to the open-chain form, followed by re-closing to form either anomer. The specific rotation of the solution changes during this process until it reaches an equilibrium ratio of the anomers.
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03:06Mechanism
Specific Rotation
Specific rotation is a property of chiral compounds that quantifies the degree to which they rotate plane-polarized light. It is expressed in degrees and is influenced by the concentration of the solution and the path length of the light. For glucose, the specific rotation can be used to determine the ratio of α and β anomers in solution, as each anomer has a distinct specific rotation.
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05:43Specific rotation vs. observed rotation.
Related Practice
Textbook Question
(a) Suggest an arrow-pushing mechanism for the mutarotation of α-d-glucose to β-d-glucose in the presence of acid. Acid isn’t necessary, but it does increase the rate of the process.
(b) What is the role of acid in your mechanism?
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Textbook Question
The α- and β-anomers of glucose are shown here. In solution, these two epimers can interconvert through a process called mutarotation.
Given that α-D-glucose has a specific rotation of + 112.2° , why is the specific rotation of β-D-glucose not -112.2°? What molecule would have a specific rotation of -112.2°?
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Textbook Question
A derivative of chitin, called chitosan, is sometimes incorporated into bandages to aid healing. Propose a reaction to convert the chitin dimer into a chitosan dimer. [Note: The glycoside linkage is unstable in acid.]
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Textbook Question
Upon dissolving α-D-glucose or β-D-glucose in water, the specific rotation gradually changes, eventually reaching +52.6° for both solutions. Explain what is happening here.
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Textbook Question
Is the compound d or l?
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