Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

16. Conjugated Systems

Cumulative Electrocyclic Problems

Organic Chemistry

16. Conjugated Systems

Cumulative Electrocyclic Problems

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6:59 minutes

Problem 7b

Textbook Question

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 guidance

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.

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.

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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