Textbook Question
Draw the product of each of the following reactions:
e.
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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 28a(1,2)
a. Name the kind of sigmatropic rearrangement that occurs in each of the following reactions.
1. 
2. 
Verified step by step guidance1
Step 1: Analyze the first reaction. The structure on the left shows a conjugated diene system with a methyl group at one end and an ethyl group at the other. Upon heating (indicated by the triangle symbol), the molecule undergoes a rearrangement where the positions of the methyl and ethyl groups are swapped. This is characteristic of a [1,5]-sigmatropic rearrangement, where a sigma bond migrates along the conjugated system.
Step 2: Understand the mechanism of the [1,5]-sigmatropic rearrangement. In this type of rearrangement, the sigma bond shifts from one position to another within the conjugated system, maintaining the overall connectivity of the molecule while redistributing substituents.
Step 3: Analyze the second reaction. The structure on the left is a bicyclic compound with a conjugated diene system. Upon heating, the molecule undergoes a rearrangement where the double bonds shift positions, and the substituents rearrange. This is characteristic of a Cope rearrangement, a specific type of [3,3]-sigmatropic rearrangement.
Step 4: Understand the mechanism of the Cope rearrangement. In this reaction, the sigma bond migrates across the conjugated system, resulting in a redistribution of the substituents and a shift in the positions of the double bonds. The reaction is thermally driven and proceeds through a cyclic transition state.
Step 5: Summarize the types of sigmatropic rearrangements observed. The first reaction is a [1,5]-sigmatropic rearrangement, while the second reaction is a [3,3]-sigmatropic rearrangement (Cope rearrangement). Both reactions are thermally induced and involve the migration of sigma bonds within conjugated systems.
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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 and a pi bond are rearranged in a concerted process. These reactions involve the migration of a substituent across a double bond, resulting in a structural change of the molecule. Understanding the mechanism and the types of sigmatropic rearrangements is crucial for predicting the products of such reactions.
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Nomenclature of Sigmatropic Shifts
Types of Sigmatropic Rearrangements
Sigmatropic rearrangements are categorized based on the number of atoms involved in the migration. The most common types are [1,3] and [1,5] rearrangements, where the numbers indicate the positions of the migrating atom relative to the original bond. Recognizing these types helps in identifying the specific rearrangement occurring in a given reaction.
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Woodward-Hoffmann Rules
The Woodward-Hoffmann rules provide a framework for predicting the stereochemical outcomes of pericyclic reactions, including sigmatropic rearrangements. These rules are based on the conservation of orbital symmetry and help determine whether a reaction is allowed or forbidden under thermal or photochemical conditions. Applying these rules is essential for understanding the feasibility of the rearrangements in the given reactions.
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1:18Woodward-Fieser Rules Example 1
Related Practice
Textbook Question
Show how the reactant can be converted to the product in two steps.
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Textbook Question
Draw the product of each of the following reactions:
d.
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Show how norbornane can be prepared from cyclopentadiene.
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Textbook Question
Account for the difference in the products of the following reactions:
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Textbook Question
Draw the product formed when each of the following compounds undergoes an electrocyclic reaction
b. under photochemical conditions.
1.
2.
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