Textbook Question
Which of the D-aldopentoses will give optically active aldaric acids on oxidation with HNO3?
Ch. 23 - Carbohydrates and Nucleic Acids
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 23, Problem 56b
Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?
(b) α-D-fructofuranosyl-β-D-mannopyranoside
Verified step by step guidance1
Step 1: Understand the concept of reducing sugars. Reducing sugars are carbohydrates that can act as reducing agents because they have a free aldehyde group (-CHO) or a free ketone group (-C=O) in their open-chain form. These sugars can reduce mild oxidizing agents like Tollens' reagent or Benedict's solution.
Step 2: Analyze the structure of the given sugar, a-D-fructofuranosyl-b-D-mannopyranoside. This is a disaccharide composed of two monosaccharides: D-fructose (a ketose) in its furanose form and D-mannose (an aldose) in its pyranose form. The two monosaccharides are linked via a glycosidic bond.
Step 3: Determine if the glycosidic bond involves the anomeric carbons of both monosaccharides. In this case, the glycosidic bond connects the anomeric carbon of D-fructose (C2) and the anomeric carbon of D-mannose (C1). Since both anomeric carbons are involved in the bond, neither monosaccharide has a free anomeric carbon, meaning the disaccharide cannot act as a reducing sugar.
Step 4: Understand the concept of mutarotation. Mutarotation is the change in optical rotation due to the interconversion between alpha and beta anomers of a sugar in solution. For mutarotation to occur, the sugar must have a free anomeric carbon that can open to form the linear structure and then reclose to form either the alpha or beta anomer.
Step 5: Conclude whether mutarotation occurs for the given sugar. Since both anomeric carbons are involved in the glycosidic bond, the sugar cannot undergo mutarotation because neither monosaccharide can open to form the linear structure. Therefore, a-D-fructofuranosyl-b-D-mannopyranoside is neither a reducing sugar nor capable of undergoing mutarotation.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Reducing Sugars
Reducing sugars are carbohydrates that can donate electrons to other molecules, typically due to the presence of a free aldehyde or ketone group. This property allows them to reduce certain chemical reagents, such as Benedict's or Fehling's solution. Common examples include glucose and fructose, which can exist in open-chain forms that contain these reactive groups.
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Reducing Sugars
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 sugars like glucose and fructose, as it leads to a mixture of anomers in solution. The rate of mutarotation can be influenced by factors such as temperature and concentration.
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Furanose and Pyranose Forms
Furanose and pyranose refer to the cyclic forms of sugars, where furanose is a five-membered ring and pyranose is a six-membered ring. The structure of the sugar affects its reactivity and properties, including whether it can act as a reducing sugar. In the case of the sugar mentioned in the question, understanding its ring structure is crucial for determining its reducing ability and mutarotation behavior.
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Related Practice
Textbook Question
Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?
(a) methyl β-D-glucopyranoside
(b) 2,3,4,6-tetra-O-methyl-D-mannopyranose
(c) 1,3,6-tri-O-methyl-D-fructofuranose
(d) methyl 2,3,4,6-tetra-O-methyl-β-D-galactopyranoside
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Textbook Question
Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?
(c) 6-O-(β-D-galactopyranosyl)-D-glucopyranose
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Textbook Question
Erwin Chargaff’s discovery that DNA contains equimolar amounts of guanine and cytosine and also equimolar amounts of adenine and thymine has come to be known as Chargaff’s rule:
G = C and A = T
(a) Does Chargaff’s rule imply that equal amounts of guanine and adenine are present in DNA? That is, does G = A?
(b) Does Chargaff’s rule imply that the sum of the purine residues equals the sum of the pyrimidine residues? That is, does A + G = C + T?
(c) Does Chargaff’s rule apply only to double-stranded DNA, or would it also apply to each individual strand if the double helical strand were separated into its two complementary strands?
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Textbook Question
An unknown reducing disaccharide is found to be unaffected by invertase enzymes. Treatment with an α-galactosidase cleaves the disaccharide to give one molecule of D-fructose and one molecule of D-galactose. When the disaccharide is treated with excess iodomethane and silver oxide and then hydrolyzed in dilute acid, the products are 2,3,4,6-tetra-O-methylgalactose and 1,3,4-tri-O-methylfructose. Propose a structure for this disaccharide, and give its complete systematic name.
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Textbook Question
Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?
(a) 4-O-(α-D-glucopyranosyl)-D-galactopyranose
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