Textbook Question
Reduction of an alkyne using the Lindlar catalyst, a reaction presented in Section 10.6.2, produces only the cis-alkene. Why?
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Ch. 22 - Conjugated Systems II: Pericyclic Reactions
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 21, Problem 10
Diene A participates in a fast and efficient Diels–Alder reaction with maleic anhydride, the powerful dienophile from Assessment 22.9. However, the related diene B does not undergo a Diels–Alder reaction. Why?
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Identify the structural features of diene A and diene B. Diene A should have a conjugated system of double bonds, which is necessary for the Diels–Alder reaction. Diene B may lack this feature.
Examine the stereochemistry and conformation of diene A. For a Diels–Alder reaction to occur, the diene must be in an s-cis conformation, allowing the p orbitals to overlap effectively with the dienophile.
Analyze the electronic properties of diene A and diene B. Diene A should have electron-rich double bonds, which are more reactive towards the electron-poor dienophile, maleic anhydride.
Consider any steric hindrance in diene B that might prevent it from adopting the necessary s-cis conformation or from effectively interacting with the dienophile.
Conclude that diene B does not undergo the Diels–Alder reaction due to its inability to meet one or more of the necessary conditions: lack of conjugation, improper conformation, unfavorable electronic properties, or steric hindrance.
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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 between a conjugated diene and a dienophile, forming a six-membered ring. It is a pericyclic reaction that occurs via a concerted mechanism, requiring the diene to be in an s-cis conformation for effective overlap of p-orbitals. This reaction is stereospecific and often used in synthetic organic chemistry to construct complex cyclic structures.
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Diels-Alder Retrosynthesis
Conformation of Dienes
Dienes can exist in s-cis or s-trans conformations, which significantly affect their reactivity in Diels–Alder reactions. The s-cis conformation allows the diene's p-orbitals to align properly with the dienophile, facilitating the cycloaddition. If a diene is locked in an s-trans conformation or cannot easily adopt the s-cis conformation, it will not participate effectively in the Diels–Alder reaction.
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Electronic Effects in Dienes
The electronic nature of a diene influences its reactivity in Diels–Alder reactions. Electron-rich dienes are more reactive as they can better interact with electron-deficient dienophiles like maleic anhydride. Substituents on the diene can alter its electron density, affecting its ability to participate in the reaction. Diene B may lack the necessary electronic properties or conformation to react with maleic anhydride.
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Related Practice
Textbook Question
We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.
(c)
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Textbook Question
In each Diels–Alder reaction shown, predict the product that will result.
(c)
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Textbook Question
We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.
(b)
1
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Textbook Question
We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.
(d)
1
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Textbook Question
In each Diels–Alder reaction shown, predict the product that will result.
(a)
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