Textbook Question
b. Using arrows, show the electron rearrangement that takes place in each reaction.
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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 12a(4)
a. Name the kind of sigmatropic rearrangement that occurs in each of the following reactions.
4. 
Verified step by step guidance1
Step 1: Understand the concept of sigmatropic rearrangements. These are pericyclic reactions where a sigma bond adjacent to one or more π systems migrates to a new position, with the π system reorganizing itself. The reaction is classified as [m,n], where m and n represent the number of atoms in the two fragments involved in the rearrangement.
Step 2: Analyze the structure of the starting material and the product. Identify the sigma bond that is breaking and the new sigma bond that is forming. Count the number of atoms in the two fragments (m and n) to determine the type of rearrangement.
Step 3: Check for common types of sigmatropic rearrangements, such as the [1,3]-hydride shift, [1,5]-hydride shift, [3,3]-Claisen rearrangement, or [3,3]-Cope rearrangement. Match the observed changes in the molecule to one of these known rearrangements.
Step 4: Verify the reaction mechanism. Ensure that the rearrangement follows the rules of orbital symmetry and conservation of aromaticity (if applicable). This step confirms that the reaction is thermally allowed under the Woodward-Hoffmann rules.
Step 5: Assign the name of the sigmatropic rearrangement based on the analysis. For example, if the reaction involves a [3,3] shift, it could be a Claisen or Cope rearrangement depending on the functional groups involved.
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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 π bond are rearranged in a concerted manner. These reactions involve the migration of a substituent across a σ-bond, leading to the formation of new bonds and the reorganization of the molecular structure. 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]-sigmatropic rearrangements, where the numbers indicate the positions of the migrating atoms. Each type has distinct characteristics and stereochemical outcomes, which are essential for 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 will proceed under thermal or photochemical conditions. Familiarity with these rules is vital for understanding the feasibility and selectivity of sigmatropic rearrangements.
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1:18Woodward-Fieser Rules Example 1
Related Practice
Textbook Question
Compare the reaction between 2,4,6-cycloheptatrienone and cyclopentadiene to the reaction between 2,4,6-cycloheptatrienone and ethene. Why does 2,4,6-cycloheptatrienone use two electrons in one reaction and four electrons in the other?
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Textbook Question
Explain why maleic anhydride reacts rapidly with 1,3-butadiene but does not react at all with ethene under thermal conditions.
Textbook Question
a. Name the kind of sigmatropic rearrangement that occurs in each of the following reactions.
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Textbook Question
Will a concerted reaction take place between 1,3-butadiene and 2-cyclohexenone in the presence of ultraviolet light?
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Textbook Question
b. Using arrows, show the electron rearrangement that takes place in each reaction.
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