Textbook Question
Which dienophile in each pair is more reactive in a Diels–Alder reaction?
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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 Benzene
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
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Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 98a(1)
Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 98a(1)Chapter 9, Problem 98a(1)
Which dienophile in each pair is more reactive in a Diels–Alder reaction?
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Identify the general principle of the Diels–Alder reaction: The reactivity of a dienophile depends on the presence of electron-withdrawing groups (EWGs) attached to it. These groups lower the energy of the dienophile's lowest unoccupied molecular orbital (LUMO), making it more reactive toward the diene.
Examine the structure of each dienophile in the pair. Look for electron-withdrawing groups such as carbonyl groups (C=O), nitriles (-C≡N), nitro groups (-NO₂), or halogens (-X). The more EWGs present, the more reactive the dienophile.
Compare the electron-withdrawing effects of the substituents in each dienophile. For example, a dienophile with a single carbonyl group will generally be less reactive than one with two carbonyl groups or a stronger EWG like a nitro group.
Consider resonance and inductive effects. Substituents that can delocalize electron density away from the dienophile through resonance or inductive effects will enhance its reactivity. For example, a conjugated system with a carbonyl group will be more reactive than a non-conjugated system.
Rank the dienophiles in each pair based on the above analysis, identifying which one has the stronger electron-withdrawing effects and is therefore more reactive in the Diels–Alder reaction.
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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. Understanding the mechanism and the factors influencing reactivity is essential for predicting the outcome of the reaction.
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Diels-Alder Retrosynthesis
Dienophile Reactivity
Dienophiles are typically electron-deficient alkenes or alkynes that react with electron-rich dienes in the Diels–Alder reaction. The reactivity of a dienophile is influenced by its electronic properties, such as the presence of electron-withdrawing groups, which enhance its ability to accept electron density from the diene. Recognizing these factors helps in determining which dienophile in a pair is more reactive.
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Electronic Effects
Electronic effects, including inductive and resonance effects, play a crucial role in determining the reactivity of organic compounds. In the context of the Diels–Alder reaction, electron-withdrawing groups (EWGs) increase the electrophilicity of the dienophile, making it more reactive. Conversely, electron-donating groups (EDGs) can decrease reactivity. Understanding these effects is vital for predicting the preferred dienophile in a given reaction scenario.
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Related Practice
Textbook Question
Draw the resonance contributors for the phenolate ion.
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Textbook Question
Protonated cyclohexylamine has a Ka = 1 * 10-11. Using the same sequence of steps as in Problem 94, determine which is a stronger base: cyclohexylamine
or aniline.
e. Which has a greater Ka: cyclohexylammmonium ion or anilinium ion?
f. Which is a stronger acid: cyclohexylamine or aniline?
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Textbook Question
Cyclopentadiene can react with itself in a Diels–Alder reaction. Draw the endo and exo products.
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Textbook Question
e. Which has a greater Ka: cyclohexanol or phenol?
f. Which is a stronger acid: cyclohexanol or phenol?
Textbook Question
Draw the major products obtained from the reaction of one equivalent of HBr with the following compounds. For each reaction, indicate the kinetic product and the thermodynamic product.
b.
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