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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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 18a
a. Will thermal 1,3-migrations of carbon occur with retention or inversion of configuration?
Verified step by step guidance1
Understand the concept of a 1,3-migration: A 1,3-migration involves the movement of a substituent (in this case, a carbon group) from one atom to another within a molecule, specifically over a distance of three atoms. This process often occurs under thermal conditions and involves a concerted mechanism.
Recognize the stereochemical implications: In a concerted reaction mechanism, the migration of the substituent and the reorganization of bonding orbitals occur simultaneously. This means that the stereochemistry of the migrating group is directly influenced by the orbital alignment during the transition state.
Analyze the orbital interactions: During a thermal 1,3-migration, the reaction typically proceeds through a suprafacial pathway (on the same face of the molecule) if the system has a favorable orbital overlap. This suprafacial migration leads to retention of configuration at the migrating carbon center.
Consider the Woodward-Hoffmann rules: These rules help predict the stereochemical outcome of pericyclic reactions. For a thermal 1,3-migration, the reaction follows the conservation of orbital symmetry, which supports retention of configuration for the migrating group.
Conclude the stereochemical outcome: Based on the concerted mechanism, orbital interactions, and the Woodward-Hoffmann rules, thermal 1,3-migrations of carbon occur with retention of configuration at the migrating carbon center.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
1,3-Migration Mechanism
1,3-migrations refer to the rearrangement of a substituent from one carbon atom to another that is three positions away in a molecule. This process often occurs in the context of rearrangements involving carbocations or radical intermediates. Understanding the mechanism is crucial for predicting the stereochemical outcome of the migration.
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General Mechanism
Retention vs. Inversion of Configuration
Retention and inversion of configuration describe how the spatial arrangement of atoms around a chiral center changes during a reaction. Retention means the configuration remains the same, while inversion indicates a switch in the arrangement. The stereochemical outcome of a migration can depend on the nature of the intermediates and the reaction conditions.
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Thermal vs. Photochemical Reactions
Thermal reactions occur at elevated temperatures and typically involve the breaking and forming of bonds without the need for light. In contrast, photochemical reactions are driven by light energy. The conditions under which a 1,3-migration occurs can influence whether the reaction leads to retention or inversion of configuration, making it essential to consider the thermal context.
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Related Practice
Textbook Question
b. Will thermal 1,5-migrations of carbon occur with retention or inversion of configuration?
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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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Textbook Question
Show how 5-methyl-1,3-cyclopentadiene rearranges to form 1-methyl-1,3-cyclopentadiene and 2-methyl-1,3-cyclopentadiene.
Textbook Question
Does the [1,7] sigmatropic rearrangement that converts provitamin D3 to vitamin D3 involve suprafacial or antarafacial rearrangement?
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Textbook Question
Account for the difference in the products obtained under photochemical and thermal conditions:
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