Textbook Question
Predict the product of the Diels–Alder reactions shown.
(a)
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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 38c
Given the conditions, would you expect conrotatory or disrotatory ring closing/opening? Justify this on the basis of the molecular orbital picture.
(c) 
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Identify the type of pericyclic reaction involved. In this case, it is a ring-closing reaction of a hexatriene system, which is a type of electrocyclic reaction.
Determine the number of π-electrons involved in the system. The hexatriene system has 6 π-electrons.
Apply the Woodward-Hoffmann rules for electrocyclic reactions. For a thermal reaction involving 4n π-electrons (where n is an integer), the reaction proceeds via a conrotatory mechanism.
Visualize the molecular orbitals involved. In a conrotatory process, the terminal p orbitals rotate in the same direction, either both clockwise or both counterclockwise, to form the new σ-bond.
Justify the mechanism based on the symmetry of the highest occupied molecular orbital (HOMO). For 6 π-electrons, the HOMO is symmetric, which supports a conrotatory closure under thermal conditions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Conrotatory and Disrotatory Motion
Conrotatory and disrotatory motions describe the stereochemical outcomes of electrocyclic reactions. In conrotatory motion, the substituents at the termini of the reacting pi system rotate in the same direction, while in disrotatory motion, they rotate in opposite directions. The type of motion depends on the number of pi electrons and whether the reaction is thermal or photochemical.
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Two Steps to Predicting Any Electrocyclic Products
Woodward-Hoffmann Rules
The Woodward-Hoffmann rules predict the stereochemistry of pericyclic reactions, including electrocyclic reactions, based on the conservation of orbital symmetry. For thermal reactions, a system with 4n pi electrons undergoes conrotatory closure, while a system with 4n+2 pi electrons undergoes disrotatory closure. These rules help determine the stereochemical outcome of the reaction.
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1:18Woodward-Fieser Rules Example 1
Molecular Orbital Theory
Molecular orbital (MO) theory explains the behavior of electrons in molecules in terms of orbitals that extend over the entire molecule. In electrocyclic reactions, the symmetry and phase of the frontier molecular orbitals (HOMO and LUMO) determine the allowed stereochemical pathway. The interaction of these orbitals during the reaction dictates whether the process is conrotatory or disrotatory.
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08:41Review of Molecular Orbitals
Related Practice
Textbook Question
Provide a mechanism of the Diels–Alder reaction shown and predict the regioisomer that will form.
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Textbook Question
Draw the products you’d expect to form in Assessment 22.38.
(c)
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Textbook Question
Predict the product of the Cope reactions shown.
(a)
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Textbook Question
For the following electrocyclic reactions, did the substituents move in a conrotatory or disrotatory direction? Would you use heat or light to cause movement in this direction?
(a)
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Textbook Question
Predict the product of the Cope reactions shown.
(c)
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