Textbook Question
a. Will thermal 1,3-migrations of carbon occur with retention or inversion of configuration?
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Ch. 28 - Pericyclic Reactions
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- 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
Chapter 25, Problem 19
Does the [1,7] sigmatropic rearrangement that converts provitamin D3 to vitamin D3 involve suprafacial or antarafacial rearrangement?
Verified step by step guidance1
Understand the [1,7] sigmatropic rearrangement: A sigmatropic rearrangement is a pericyclic reaction where a sigma bond migrates across a conjugated π-system. The [1,7] notation indicates that the migrating group moves from the first atom to the seventh atom in the conjugated system.
Analyze the molecular orbital symmetry: In a [1,7] sigmatropic rearrangement, the reaction involves the breaking and forming of sigma bonds while maintaining the π-system. The reaction's stereochemistry depends on whether the rearrangement is suprafacial (same face of the π-system) or antarafacial (opposite face of the π-system).
Consider the geometry of the system: For a [1,7] rearrangement, the π-system spans a significant distance. An antarafacial rearrangement would require the system to adopt a highly strained geometry, which is typically unfavorable in such large systems.
Apply the Woodward-Hoffmann rules: These rules predict the stereochemistry of pericyclic reactions based on orbital symmetry. For a [1,7] sigmatropic rearrangement, the reaction is thermally allowed and typically proceeds via a suprafacial pathway due to the favorable orbital overlap and lower strain.
Conclude the stereochemical pathway: Based on the analysis, the [1,7] sigmatropic rearrangement that converts provitamin D3 to vitamin D3 involves a suprafacial rearrangement, as this is the most favorable pathway for this reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Sigmatropic Rearrangement
Sigmatropic rearrangements are a class of pericyclic reactions where a sigma bond is broken and reformed, resulting in the migration of a substituent. These reactions can be classified based on the orientation of the migrating group relative to the original bond, leading to suprafacial or antarafacial pathways. Understanding the mechanism of these rearrangements is crucial for predicting the product structure and stereochemistry.
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Nomenclature of Sigmatropic Shifts
Suprafacial vs. Antarafacial Rearrangement
In a suprafacial rearrangement, the migrating group moves along the same face of the molecule, maintaining its orientation relative to the original bond. Conversely, an antarafacial rearrangement involves the migrating group moving to the opposite face, which can lead to different stereochemical outcomes. Identifying which type of rearrangement occurs is essential for understanding the reaction mechanism and the final product.
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Provitamin D3 to Vitamin D3 Conversion
The conversion of provitamin D3 to vitamin D3 involves a [1,7] sigmatropic rearrangement, where the structure undergoes a shift in the position of the double bond and the associated substituents. This transformation is significant in biochemistry as it relates to the synthesis of vitamin D3, which plays a vital role in calcium metabolism and bone health. Analyzing the rearrangement type helps in understanding the reaction's stereochemical implications.
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Related Practice
Textbook Question
Explain why [1,3] sigmatropic migrations of hydrogen cannot occur under thermal conditions, but [1,3] sigmatropic migrations of carbon can.
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Textbook Question
b. Will thermal 1,5-migrations of carbon occur with retention or inversion of configuration?
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Textbook Question
Draw the product of each of the following reactions:
d.
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Textbook Question
Chorismate mutase is an enzyme that promotes a pericyclic reaction by forcing the substrate to assume the conformation needed for the reaction. The product of the pericyclic reaction is prephenate that is subsequently converted into the amino acids phenylalanine and tyrosine. What kind of a pericyclic reaction does chorismate mutase catalyze?
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Textbook Question
Explain why the hydrogen and the methyl substituent are trans to one another after photochemical ring closure of provitamin D3 to form 7-dehydrocholesterol.
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