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 17a,b
Wade 9th EditionCh. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet SpectroscopyProblem 17a,bChapter 15, Problem 17a,b
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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Identify the reactants in each image. In the first image, the reactants are isoprene (2-methyl-1,3-butadiene) and methyl vinyl ketone. In the second image, the reactants are methoxybutadiene and acrylonitrile.
For each pair of reactants, consider the possibility of a Diels-Alder reaction, which involves a diene and a dienophile. The diene is the compound with two double bonds, and the dienophile is the compound with one double bond and an electron-withdrawing group.
Draw the resonance structures for the diene and the dienophile. For the diene, show the movement of electrons to form a charge-separated structure. For the dienophile, show the electron-withdrawing group stabilizing the negative charge.
For the first pair, isoprene can form a resonance structure where one of the double bonds shifts, creating a positive charge on one carbon and a negative charge on another. Methyl vinyl ketone can form a resonance structure where the carbonyl group stabilizes a negative charge.
For the second pair, methoxybutadiene can form a resonance structure with a positive charge on the carbon adjacent to the methoxy group and a negative charge on the terminal carbon. Acrylonitrile can form a resonance structure where the cyano group stabilizes a negative charge.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Resonance Structures
Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. They help in understanding the distribution of charge and the stability of a molecule. In organic chemistry, resonance is crucial for predicting the behavior of reactants and products, especially in reactions involving conjugated systems.
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Drawing Resonance Structures
Charge Separation
Charge separation refers to the distribution of positive and negative charges within a molecule. In resonance forms, charge separation can indicate the stability of a compound; structures with minimized charge separation are generally more stable. Understanding charge separation is essential for predicting the reactivity and product formation in organic reactions.
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Substituent Positioning
The positioning of substituents on a molecule significantly influences its chemical properties and reactivity. In the context of the question, the 1,2- and 1,4-relationships refer to the relative positions of substituents on a benzene ring or similar structure. Recognizing these relationships is vital for predicting the outcomes of reactions and understanding the stability of the resulting products.
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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
What dienes and dienophiles would react to give the following Diels–Alder products?
(d)
(e)
(f)
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Textbook Question
What dienes and dienophiles would react to give the following Diels–Alder products?
(a)
(b)
(c)
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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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Textbook Question
Predict the products of the following Diels–Alder reactions.
(a)
(b)
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