Textbook Question
Predict the products obtained when D-galactose reacts with each reagent.
(h) NaBH4
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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 52k
Predict the products obtained when D-galactose reacts with each reagent.
(k) excess HIO4
Verified step by step guidance1
Understand the reaction: Periodic acid (HIO4) is an oxidizing agent that cleaves vicinal diols (two hydroxyl groups on adjacent carbons) in carbohydrates. It breaks the C-C bond between the carbons bearing the hydroxyl groups, forming smaller carbonyl-containing fragments such as aldehydes or formic acid.
Analyze the structure of D-galactose: D-galactose is an aldohexose, meaning it has six carbons, with an aldehyde group at C1 and hydroxyl groups on the other carbons. Draw the Fischer projection of D-galactose to visualize the vicinal diols.
Identify the vicinal diols: In D-galactose, vicinal diols are present between C2-C3, C3-C4, C4-C5, and C5-C6. These are the sites where HIO4 will cleave the C-C bonds.
Determine the cleavage products: For each vicinal diol, the C-C bond is broken, and each carbon forms a carbonyl group. Depending on the position of the carbon, the products will be either formaldehyde (HCHO), formic acid (HCOOH), or a larger aldehyde/ketone.
Combine the results: After cleaving all vicinal diols in excess HIO4, the D-galactose molecule will be completely broken down into smaller fragments. Write out the specific products formed from each cleavage site to complete the reaction analysis.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
D-Galactose Structure
D-galactose is a six-carbon aldose sugar with a specific stereochemistry. It contains an aldehyde group at one end and multiple hydroxyl groups, which influence its reactivity. Understanding its structure is crucial for predicting how it will react with various reagents, including oxidative agents like HIO4.
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Monosaccharides - D and L Isomerism
Periodic Acid Oxidation
Periodic acid (HIO4) is a strong oxidizing agent that cleaves vicinal diols and aldehydes. In the case of sugars, it can oxidatively cleave the carbon-carbon bonds adjacent to hydroxyl groups, leading to the formation of smaller aldehydes or ketones. This reaction is essential for understanding the products formed when d-galactose is treated with excess HIO4.
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04:15Monosaccharides - Weak Oxidation (Aldonic Acid)
Reaction Mechanism
The reaction mechanism describes the step-by-step process by which reactants are converted into products. For d-galactose reacting with HIO4, the mechanism involves the formation of cyclic intermediates and subsequent cleavage of the sugar backbone. A clear grasp of these mechanisms helps in predicting the final products of the reaction.
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Related Practice
Textbook Question
Draw the structures (using chair conformations of pyranoses) of the following disaccharides.
(a) 4-O-(α-D-glucopyranosyl)-D-galactopyranose
(b) α-D-fructofuranosyl-β-D-mannopyranoside
(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
Predict the products obtained when D-galactose reacts with each reagent.
(i) Br2, H2O, then H2O2 and Fe2(SO4)3
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Textbook Question
Draw the following sugar derivatives.
(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
Predict the products obtained when D-galactose reacts with each reagent.
(j) (1) KCN/HCN; (2) H2, Pd/BaSO4; (3) H3O+
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