Domanda del libro di testo
Draw the mechanism for the interconversion of α-D-glucose and β-D-glucose in dilute HCl.
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Ch. 20 - The Organic Chemistry of Carbohydrates
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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TOC.tableOfContents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding31
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds: Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
Capitolo 20, Problema 44
Treatment with sodium borohydride converts aldose A to an optically inactive alditol. Wohl degradation of A forms B, whose alditol is optically inactive. Wohl degradation of B forms D-glyceraldehyde. Identify A and B.
Guida verificata passo dopo passo1
Step 1: Understand the problem. Sodium borohydride (NaBH₄) reduces aldoses to alditols by converting the aldehyde group (-CHO) into a primary alcohol (-CH₂OH). The fact that the alditol of A is optically inactive suggests that A is a meso compound, meaning it has internal symmetry and no net optical activity.
Step 2: Perform the first Wohl degradation. Wohl degradation involves converting an aldose into a smaller aldose by removing the terminal carbon atom as hydrogen cyanide (HCN). The fact that the alditol of B is also optically inactive suggests that B is also a meso compound.
Step 3: Perform the second Wohl degradation. The problem states that the second Wohl degradation of B produces d-glyceraldehyde. This is a key clue because d-glyceraldehyde is the simplest aldose with a single chiral center, and it is optically active.
Step 4: Work backward to identify B. Since B undergoes Wohl degradation to form d-glyceraldehyde, B must be a four-carbon aldose (aldotetrose) with internal symmetry. The only meso aldotetrose is erythrose, which has two chiral centers and internal symmetry.
Step 5: Work backward to identify A. Since A undergoes Wohl degradation to form B (erythrose), A must be a five-carbon aldose (aldopentose) with internal symmetry. The only meso aldopentose is ribose. Therefore, A is ribose, and B is erythrose.
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Aldoses and Alditols
Aldoses are a type of monosaccharide that contain an aldehyde group, while alditols are sugar alcohols formed by the reduction of aldoses. The conversion of an aldose to an alditol typically involves the addition of hydrogen to the carbonyl group, resulting in a compound that lacks optical activity if it has a symmetrical structure.
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07:19
Monosaccharides - Reduction (Alditols)
Wohl Degradation
Wohl degradation is a chemical reaction that involves the oxidative cleavage of aldoses to produce smaller aldehydes or ketones. This process is significant in carbohydrate chemistry as it allows for the identification and transformation of sugars, leading to the formation of simpler sugars like d-glyceraldehyde from more complex aldoses.
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09:43Monosaccharides - Wohl Degradation
Optical Activity
Optical activity refers to the ability of a compound to rotate plane-polarized light, which is a characteristic of chiral molecules. A compound is optically inactive if it is either achiral or if it contains a plane of symmetry, resulting in equal contributions to light rotation from its enantiomers. Understanding optical activity is crucial for identifying the stereochemistry of sugars and their derivatives.
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08:17Mutarotation and Optical Activity
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