Textbook Question
Make a model of cyclooctatetraene in the tub conformation. Draw this conformation, and estimate the angle between the p orbitals of adjacent pi bonds.
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Ch. 16 - Aromatic Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 16, Problem 4
Show the product of the Diels–Alder dimerization of cyclobutadiene. (This reaction is similar to the dimerization of cyclopentadiene, discussed in Section 15-11.)
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Identify the reactants: Cyclobutadiene is the diene in this reaction. It is a highly reactive compound due to its antiaromaticity (4π electrons). The Diels–Alder reaction involves a diene and a dienophile, but in this case, cyclobutadiene acts as both the diene and the dienophile.
Analyze the reaction mechanism: The Diels–Alder reaction is a [4+2] cycloaddition, where four π-electrons from the diene interact with two π-electrons from the dienophile to form a new six-membered ring. Cyclobutadiene will react with another molecule of itself to form a dimer.
Draw the interaction: Orient one molecule of cyclobutadiene as the diene (with conjugated double bonds) and the other as the dienophile (with one double bond acting as the π-system). The π-electrons from the diene will overlap with the π-electrons of the dienophile.
Predict the product: The reaction will result in the formation of a bicyclic compound. Specifically, the product will be a bicyclo[2.2.0]hexadiene structure, where the two cyclobutadiene units are fused together to form a six-membered ring with two double bonds.
Verify stereochemistry and stability: Since cyclobutadiene is highly reactive and unstable, the dimerization helps relieve some of the antiaromaticity. Ensure that the product structure is consistent with the rules of the Diels–Alder reaction and that all bonds are correctly formed.
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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. This reaction is characterized by its stereospecificity and is widely used in organic synthesis to create complex cyclic structures. Understanding the mechanism involves recognizing the roles of electron-rich and electron-poor species in the reaction.
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Cyclobutadiene
Cyclobutadiene is a four-membered cyclic compound with alternating double bonds, making it a highly reactive diene. Due to its antiaromatic nature, it is unstable and tends to dimerize or undergo other reactions quickly. Its behavior in the Diels–Alder reaction is significant because it can act as a diene, leading to the formation of larger cyclic products.
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Dimerization
Dimerization refers to the process where two identical molecules combine to form a dimer, which is a larger compound. In the context of cyclobutadiene, dimerization can occur through the Diels–Alder reaction, resulting in a stable product from two reactive diene units. This concept is crucial for predicting the outcome of reactions involving unstable intermediates like cyclobutadiene.
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Related Practice
Textbook Question
a. Draw the resonance forms of benzene, cyclobutadiene, and cyclooctatetraene, showing all the carbon and hydrogen atoms.
b. Assuming that these molecules are all planar, show how the p orbitals on the sp2 hybrid carbon atoms form continuous rings of overlapping orbitals above and below the plane of the carbon atoms.
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Textbook Question
Using the information in Figure 16-2, calculate the values of ∆H° for the following reactions:
(b)
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Textbook Question
Classify the following compounds as aromatic, antiaromatic, or nonaromatic.
(a)
(b)
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Textbook Question
Does the MO energy diagram of cyclooctatetraene (Figure 16-8) appear to be a particularly stable or unstable configuration? Explain.
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Textbook Question
Using the information in Figure 16-2, calculate the values of ∆H° for the following reactions:
(c)
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