Textbook Question
b. Are the indicated hydrogens cis or trans?
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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 9
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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Verified step by step guidance1
Step 1: Analyze the reaction between 2,4,6-cycloheptatrienone and cyclopentadiene. This reaction is a Diels-Alder reaction, where cyclopentadiene acts as the diene (providing four π electrons) and 2,4,6-cycloheptatrienone acts as the dienophile (providing two π electrons). The reaction forms a bicyclic compound with a new six-membered ring.
Step 2: Analyze the reaction between 2,4,6-cycloheptatrienone and ethene. This reaction is a [2+2] cycloaddition, where ethene provides two π electrons and 2,4,6-cycloheptatrienone also contributes two π electrons. The reaction forms a four-membered ring fused to the cycloheptatrienone structure.
Step 3: Understand why 2,4,6-cycloheptatrienone uses different numbers of π electrons in these reactions. In the Diels-Alder reaction, the conjugated π system of cyclopentadiene interacts with the π system of 2,4,6-cycloheptatrienone, allowing the use of four π electrons from the diene and two π electrons from the dienophile. In the [2+2] cycloaddition with ethene, only two π electrons from each reactant are involved.
Step 4: Consider the electronic structure of 2,4,6-cycloheptatrienone. The molecule has a conjugated π system, but its reactivity depends on the type of reaction and the nature of the other reactant. In the Diels-Alder reaction, the extended conjugation of cyclopentadiene matches the π system of 2,4,6-cycloheptatrienone, while in the [2+2] cycloaddition, ethene's simpler π system limits the interaction to two π electrons.
Step 5: Summarize the key difference. The number of π electrons used by 2,4,6-cycloheptatrienone depends on the type of cycloaddition reaction and the electronic compatibility of the reactants. The Diels-Alder reaction involves a [4+2] interaction, while the [2+2] cycloaddition involves a simpler interaction between two π electrons from each reactant.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Diels-Alder Reaction
The Diels-Alder reaction is a [4+2] cycloaddition reaction between a conjugated diene and a dienophile, resulting in the formation of a six-membered ring. In this context, cyclopentadiene acts as the diene, while 2,4,6-cycloheptatrienone serves as the dienophile. This reaction is significant for understanding how p electrons are utilized in forming new bonds during the reaction.
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Diels-Alder Retrosynthesis
Electrophilicity and Nucleophilicity
Electrophilicity refers to the ability of a species to accept electrons, while nucleophilicity is the ability to donate electrons. In the reactions mentioned, 2,4,6-cycloheptatrienone acts as an electrophile when reacting with cyclopentadiene, which is a nucleophile. The difference in the number of p electrons used in each reaction can be attributed to the varying strengths of the electrophilic and nucleophilic components.
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Conjugation and Resonance
Conjugation involves the overlap of p orbitals across adjacent double bonds, leading to increased stability through resonance. In the case of 2,4,6-cycloheptatrienone, the presence of multiple double bonds allows for resonance stabilization, which influences how many p electrons are involved in different reactions. This concept is crucial for understanding the reactivity patterns of the compounds in question.
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Related Practice
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
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
a. Identify the mode of ring closure for each of the following electrocyclic reactions
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Textbook Question
a. Name the kind of sigmatropic rearrangement that occurs in each of the following reactions.
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Textbook Question
b. Are the indicated hydrogens cis or trans?
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