Textbook Question
a. Identify the mode of ring closure for each of the following electrocyclic reactions
1.
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Ch. 28 - Pericyclic Reactions
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
Chapter 25, Problem 7b
Which of the following are correct? Correct any false statements.
b. A conjugated diene with an antisymmetric HOMO undergoes conrotatory ring closure under thermal conditions.
Verified step by step guidance1
Step 1: Understand the problem. The question involves the Woodward-Hoffmann rules, which predict the stereochemical outcome of pericyclic reactions (e.g., electrocyclic reactions). Specifically, it asks about the behavior of a conjugated diene undergoing a ring closure under thermal conditions.
Step 2: Recall the key concept. For electrocyclic reactions, the stereochemical outcome depends on the number of π-electrons in the system and whether the reaction occurs under thermal or photochemical conditions. The Woodward-Hoffmann rules state: (1) For a system with 4n π-electrons, thermal conditions favor conrotatory motion, while photochemical conditions favor disrotatory motion. (2) For a system with 4n+2 π-electrons, the opposite is true.
Step 3: Analyze the given system. A conjugated diene has 4 π-electrons (n=1). Under thermal conditions, the reaction will proceed via conrotatory motion, as per the Woodward-Hoffmann rules. This aligns with the statement in the problem.
Step 4: Evaluate the HOMO symmetry. The HOMO (Highest Occupied Molecular Orbital) of a conjugated diene is symmetric under thermal conditions. An antisymmetric HOMO would not align with the conrotatory motion required for thermal ring closure. Therefore, the statement in the problem is false.
Step 5: Correct the false statement. The corrected statement should read: 'A conjugated diene with a symmetric HOMO undergoes conrotatory ring 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.
Conjugated Dienes
Conjugated dienes are organic compounds that contain two double bonds separated by a single bond. This arrangement allows for delocalization of π electrons, which can stabilize the molecule and influence its reactivity. Understanding the structure and properties of conjugated dienes is crucial for predicting their behavior in reactions, such as cyclization.
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Conjugated states
HOMO and LUMO
The Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) are key concepts in molecular orbital theory. The HOMO is the highest energy orbital that contains electrons, while the LUMO is the lowest energy orbital that is empty. The interaction between these orbitals during reactions, such as cyclization, determines the mechanism and outcome of the reaction, including whether it proceeds via conrotatory or disrotatory pathways.
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02:35HOMO vs. LUMO
Conrotatory vs. Disrotatory Closure
Conrotatory and disrotatory closures refer to the two possible ways that a diene can cyclize to form a ring. In conrotatory closure, the ends of the diene rotate in the same direction, while in disrotatory closure, they rotate in opposite directions. The type of closure that occurs is influenced by the symmetry of the HOMO; for example, an antisymmetric HOMO typically leads to disrotatory closure under thermal conditions, making the statement in the question incorrect.
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Related Practice
Textbook Question
Which of the following are correct? Correct any false statements.
a. A conjugated diene with an even number of double bonds undergoes conrotatory ring closure under thermal conditions.
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Textbook Question
c. Under photochemical conditions, will ring closure be conrotatory or disrotatory?
d. Will the product have the cis or the trans configuration?
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Textbook Question
a. Under thermal conditions, will ring closure of (2E,4Z,6Z,8E)-2,4,6,8-decatetraene be conrotatory or disrotatory?
b. Will the product have the cis or the trans configuration?
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Textbook Question
a. Identify the mode of ring closure for each of the following electrocyclic reactions
2.
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Textbook Question
Which of the following are correct? Correct any false statements
c. A conjugated diene with an odd number of double bonds has a symmetric HOMO.
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