Textbook Question
The Eschenmoser–Claisen reaction is a variant of the Claisen reaction studied in this chapter. Based on your answers to Assessments 22.53–22.55, predict a product of this reaction.
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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 58
In Chapter 20, we studied the aldol reaction. Although not discussed at the time, this reaction is stereospecific, proceeding through the Zimmerman–Traxler transition state shown here.
(a) Show an arrow-pushing mechanism for this concerted reaction.
(b) Why is this a favorable mechanism?
Verified step by step guidance1
Identify the reactants and the product in the aldol reaction. The reactants are a benzaldehyde and a lithium enolate, and the product is a β-hydroxy ketone.
Understand the Zimmerman–Traxler transition state, which is a six-membered chair-like transition state. This state is crucial for the stereospecificity of the reaction.
Draw the arrow-pushing mechanism: Start by showing the nucleophilic attack of the enolate carbon (C2) on the carbonyl carbon (C4) of the benzaldehyde. This forms a new C-C bond.
Simultaneously, show the movement of electrons from the carbonyl oxygen (O) to form a partial bond with lithium (Li), stabilizing the transition state.
Explain why this mechanism is favorable: The chair-like transition state minimizes steric hindrance and allows for the formation of a stable six-membered ring, which is energetically favorable. Additionally, the partial bonds help stabilize the transition state, making the reaction more efficient.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aldol Reaction
The aldol reaction is a fundamental carbon-carbon bond-forming reaction in organic chemistry, involving the nucleophilic addition of an enolate ion to a carbonyl compound. This reaction typically results in the formation of a β-hydroxy carbonyl compound, which can further undergo dehydration to yield an α,β-unsaturated carbonyl compound. Understanding the mechanism and stereochemistry of this reaction is crucial for predicting product formation.
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Crossed Aldol
Zimmerman–Traxler Transition State
The Zimmerman–Traxler transition state is a model used to explain the stereochemistry of certain aldol reactions. It describes a six-membered, chair-like transition state where the enolate and aldehyde are aligned in a specific orientation, leading to stereospecific outcomes. This model helps predict the stereochemical configuration of the aldol product based on the geometry of the transition state, emphasizing the importance of steric and electronic factors.
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Arrow-Pushing Mechanism
Arrow-pushing is a technique used to illustrate the movement of electrons during chemical reactions, particularly in organic chemistry. It involves using curved arrows to show the flow of electron pairs, helping to visualize how bonds are formed and broken. In the context of the aldol reaction, arrow-pushing is essential for understanding the step-by-step mechanism, including the formation of the enolate and its subsequent attack on the carbonyl group.
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Related Practice
Textbook Question
The product of the Stille coupling reaction (A) tautomerizes in a basic solution to give compound B. B spontaneously converts to C.
(c) Suggest a mechanism for the conversion of B to C
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Textbook Question
Only after working Assessment 22.53, predict the product of the following reactions.
(b)
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Textbook Question
The product of the Stille coupling reaction (A) tautomerizes in a basic solution to give compound B. B spontaneously converts to C. (a) Propose a structure for A. (b) Suggest a mechanism for the conversion of A to B.
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Textbook Question
The Johnson–Claisen reaction is a variant of the Claisen reaction studied in this chapter. (a) Suggest a mechanism for the first step. (b) Predict the product (B) that would result from heating intermediate A.
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Textbook Question
While not covered explicitly in this chapter, the ene reaction occurs similarly to the Diels–Alder reaction but replaces the electrons from one bond in the diene with the electrons in a C―H bond. Draw the mechanism for the following reaction. [Number the carbons and draw in the hydrogens of the product. And, of course, make a note of bonds formed and bonds broken.]
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