Textbook Question
cis-3,4-Dimethylcyclobutene undergoes thermal ring opening to form the two products shown. One of the products is formed in 99% yield, the other in 1% yield. Which is which?
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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 42
Propose a mechanism for the following reaction:
Verified step by step guidance1
Step 1: Identify the functional groups in the starting material. The molecule contains an ether group (-O-) attached to a benzene ring and an allylic group. The reaction conditions indicate heat (Δ), which suggests a rearrangement or elimination mechanism.
Step 2: Recognize the likely mechanism. Heating often promotes a Claisen rearrangement in allyl aryl ethers. This involves the migration of the allyl group to the ortho or para position of the benzene ring via a concerted pericyclic reaction.
Step 3: Draw the transition state for the Claisen rearrangement. The allyl group undergoes a [3,3]-sigmatropic rearrangement, where the bond between the oxygen and the allyl group breaks, and a new bond forms between the allyl group and the ortho position of the benzene ring.
Step 4: After the rearrangement, the intermediate formed is an ortho-allyl phenol. The hydroxyl group (-OH) is generated as the ether bond is cleaved during the rearrangement.
Step 5: Verify the final product. The structure of the product shows the allyl group attached to the ortho position of the benzene ring, and the hydroxyl group (-OH) is present on the benzene ring, confirming the Claisen rearrangement mechanism.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Claisen Rearrangement
The Claisen rearrangement is a thermal reaction involving the rearrangement of allyl aryl ethers to ortho- and para-substituted phenols. This reaction proceeds through a concerted mechanism, where the bond between the oxygen and the carbon atom is broken, and a new bond is formed, resulting in the migration of the allyl group. Understanding this rearrangement is crucial for predicting the products of the reaction shown in the image.
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Definition of Claisen Rearrangement
Mechanistic Pathway
A mechanistic pathway outlines the step-by-step sequence of events that occur during a chemical reaction. In the case of the Claisen rearrangement, it involves the formation of a cyclic transition state, where the electrons are redistributed, leading to the formation of the final product. Analyzing the mechanistic pathway helps in understanding how the reactants transform into products and the role of intermediates in the reaction.
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Thermal Activation
Thermal activation refers to the energy input required to initiate a chemical reaction, often provided by heat. In the Claisen rearrangement, heating the reaction mixture facilitates the necessary bond breaking and formation processes. Recognizing the importance of thermal activation is essential for predicting the conditions under which the reaction will proceed and for optimizing reaction yields.
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Related Practice
Textbook Question
A student found that heating any one of the isomers shown here resulted in scrambling of the deuterium to all three positions on the five-membered ring. Propose a mechanism to account for this observation.
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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
How can this transformation be carried out using only heat or light?
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Textbook Question
Explain why compound A will not undergo a ring-opening reaction under thermal conditions, but compound B will.
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