Textbook Question
Propose a mechanism for the following 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 37c
Draw the product of each of the following sigmatropic rearrangements:
c. ![Chemical structure illustrating a [5,5] sigmatropic rearrangement with a phenyl group and a diene.](https://static.studychannel-dev.pearsondev.tech/courses/organic-chemistry/thumbnails/30886d49-6415-4309-97db-2ac92f18960f)
Verified step by step guidance1
Identify the type of sigmatropic rearrangement involved. Sigmatropic rearrangements are pericyclic reactions where a sigma bond migrates across a conjugated π-system. Common examples include [1,3]-shifts, [1,5]-shifts, and the Claisen or Cope rearrangements.
Determine the numbering of the atoms involved in the rearrangement. For example, in a [3,3]-sigmatropic rearrangement, the sigma bond migrates between two sets of three atoms, maintaining the connectivity of the π-system.
Draw the starting structure and locate the sigma bond that will break and the new sigma bond that will form. Use curved arrows to show the movement of electrons during the rearrangement.
Apply the Woodward-Hoffmann rules to ensure that the rearrangement is thermally allowed. These rules are based on the conservation of orbital symmetry and help confirm whether the reaction proceeds under thermal or photochemical conditions.
Draw the product of the rearrangement, ensuring that the new sigma bond is correctly formed and the π-system is properly reconnected. Verify that the product structure is consistent with the reaction mechanism and the type of sigmatropic shift identified.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Sigmatropic Rearrangements
Sigmatropic rearrangements are a class of pericyclic reactions where a sigma bond and a pi bond undergo a concerted rearrangement. These reactions typically 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, such as [1,3] or [3,3] shifts, is crucial for predicting the products formed.
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Nomenclature of Sigmatropic Shifts
Conservation of Orbital Symmetry
Conservation of orbital symmetry is a principle that states that the symmetry of molecular orbitals must be preserved during a reaction. In sigmatropic rearrangements, this principle helps determine whether a reaction is allowed or forbidden based on the symmetry properties of the involved orbitals. Recognizing the symmetry of the reactants and products is essential for predicting the feasibility of the rearrangement.
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Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In sigmatropic rearrangements, regioselectivity can be influenced by factors such as sterics and electronic effects, which dictate the most stable product. Understanding regioselectivity is important for accurately predicting the outcome of the rearrangement and the structure of the final product.
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Related Practice
Textbook Question
Draw the product of each of the following sigmatropic rearrangements:
d.
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Textbook Question
If the compounds shown here are heated, one will form one product from a [1,3] sigmatropic rearrangement and the other will form two products from two different [1,3] sigmatropic rearrangements. Draw the products of the reactions.
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Textbook Question
Explain why two different products are formed from disrotatory ring closure of (2E,4Z,6Z)-octatriene, but only one product is formed from disrotatory ring closure of (2E,4Z,6E)-octatriene.
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Textbook Question
What is the product of the following [1,3] sigmatropic rearrangement, A or B?
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Textbook Question
b. What would be the product if trans-2-butene were used instead of ethene?
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