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 16
Show how 5-methyl-1,3-cyclopentadiene rearranges to form 1-methyl-1,3-cyclopentadiene and 2-methyl-1,3-cyclopentadiene.
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Identify the starting compound, 5-methyl-1,3-cyclopentadiene, which is a conjugated diene with a methyl group attached to the fifth carbon of the cyclopentadiene ring.
Recognize that the reaction involves a [1,5]-sigmatropic shift, a type of pericyclic reaction where a substituent (in this case, the methyl group) migrates across the conjugated π-system of the diene.
Draw the mechanism for the [1,5]-sigmatropic shift: the π-electrons of the conjugated diene rearrange, and the methyl group moves from the fifth carbon to the first carbon, forming 1-methyl-1,3-cyclopentadiene.
Consider the possibility of a second [1,5]-sigmatropic shift: the methyl group on the first carbon can migrate again across the conjugated π-system to the second carbon, forming 2-methyl-1,3-cyclopentadiene.
Verify the structures of the products (1-methyl-1,3-cyclopentadiene and 2-methyl-1,3-cyclopentadiene) to ensure that the rearrangements preserve the conjugated diene system and follow the rules of pericyclic reactions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Cyclopentadiene Structure
Cyclopentadiene is a five-membered ring compound containing two double bonds. Its structure allows for unique reactivity due to the presence of conjugated double bonds, which can participate in various rearrangements and reactions. Understanding the geometry and electronic configuration of cyclopentadiene is crucial for predicting its behavior during rearrangement.
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Drawing Resonance Structures
Rearrangement Mechanisms
Rearrangement mechanisms involve the reorganization of atoms within a molecule to form a new structure. In the case of 5-methyl-1,3-cyclopentadiene, the rearrangement can occur through a series of bond-breaking and bond-forming steps, often facilitated by the stability of intermediates. Recognizing the types of rearrangements, such as 1,2-shifts or ring expansions, is essential for understanding the transformation into 1-methyl-1,3-cyclopentadiene and 2-methyl-1,3-cyclopentadiene.
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06:08Definition of Claisen Rearrangement
Stability of Intermediates
The stability of reaction intermediates plays a significant role in determining the pathway and products of a rearrangement reaction. In this case, the formation of stable carbocation or radical intermediates can influence whether the rearrangement favors the formation of 1-methyl-1,3-cyclopentadiene or 2-methyl-1,3-cyclopentadiene. Analyzing the stability of these intermediates helps predict the outcome of the rearrangement process.
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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
Why was a deuterated compound used in the last reaction on the preceding page?
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Textbook Question
If the terminal sp2 carbon of the substituent attached to the benzene ring is labeled with 14C, where will the label be in the product?
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Textbook Question
Account for the difference in the products obtained under photochemical and thermal conditions:
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