Textbook Question
Show that the [4 + 2] Diels–Alder reaction is photochemically forbidden.
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Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy
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
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Wade 9th EditionCh. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet SpectroscopyProblem 18a,b
Wade 9th EditionCh. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet SpectroscopyProblem 18a,bChapter 15, Problem 18a,b
Predict the products of the following Diels–Alder reactions.
(a) 
(b) 
Verified step by step guidance1
Step 1: Identify the components of the Diels–Alder reaction. The reaction involves a conjugated diene and a dienophile. In image (a), the diene is the methoxy-substituted cyclopentadiene, and the dienophile is the alkyne with an ester group (COOCH₃). In image (b), the diene is the methoxy-substituted cyclohexadiene, and the dienophile is the cyclohexenone.
Step 2: Analyze the electronic effects. The methoxy group (-OCH₃) on the diene is an electron-donating group, which increases the nucleophilicity of the diene. The ester group (COOCH₃) in image (a) and the ketone group (C=O) in image (b) are electron-withdrawing groups, which enhance the electrophilicity of the dienophile.
Step 3: Predict the regioselectivity. In both cases, the electron-donating group on the diene will direct the reaction to form the most stable product. The electron-withdrawing group on the dienophile will align with the electron-rich part of the diene to maximize stabilization.
Step 4: Draw the cyclic adduct. The Diels–Alder reaction forms a six-membered ring by combining the diene and dienophile. For image (a), the product will be a bicyclic compound with the ester group attached to the newly formed ring. For image (b), the product will be a bicyclic compound with the ketone group attached to the newly formed ring.
Step 5: Consider stereochemistry. The Diels–Alder reaction is stereospecific, meaning the stereochemistry of the substituents on the diene and dienophile will be preserved in the product. Ensure that the substituents are correctly positioned in the final structure based on their original orientation.
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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 a key method in organic synthesis for constructing cyclic compounds and is characterized by its stereospecificity and regioselectivity, making it a powerful tool for chemists.
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Diene and Dienophile
In the context of the Diels–Alder reaction, a diene is a molecule containing two double bonds, while a dienophile is a compound that contains a double or triple bond and reacts with the diene. The reactivity of these components is influenced by their electronic properties, such as electron-donating or withdrawing groups, which can enhance or diminish the reaction's efficiency.
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Regioselectivity and Stereochemistry
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others, while stereochemistry involves the spatial arrangement of atoms in the resulting product. In Diels–Alder reactions, the orientation of substituents on the diene and dienophile can significantly affect the final product's structure, leading to different regioisomers and stereoisomers.
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Related Practice
Textbook Question
Predict the products of the following Diels–Alder reactions.
(c)
(d)
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Textbook Question
We predicted that the products would have a 1,2- or 1,4-relationship of the proper substituents. Draw the charge-separated resonance forms of the reactants to support these predictions.
(a) (b)
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Textbook Question
Show that the [4 + 4] cycloaddition of two butadiene molecules to give cycloocta-1,5-diene is thermally forbidden but photochemically allowed.
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Textbook Question
What dienes and dienophiles would react to give the following Diels–Alder products?
(d)
(e)
(f)
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Textbook Question
Predict the major product for each proposed Diels–Alder reaction. Include stereochemistry where appropriate.
(a)
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