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

Photochemical Electrocyclic Reactions

Organic Chemistry

16. Conjugated Systems

Photochemical Electrocyclic Reactions

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Problem 6c,d

Textbook Question

c. Under photochemical conditions, will ring closure be conrotatory or disrotatory?
d. Will the product have the cis or the trans configuration?

Verified step by step guidance

Determine the type of pericyclic reaction involved. In this case, the problem involves a ring closure, which is a type of electrocyclic reaction. Electrocyclic reactions can proceed under thermal or photochemical conditions, and the stereochemical outcome depends on the number of π-electrons in the system and the reaction conditions.

Count the number of π-electrons in the conjugated system undergoing the ring closure. Use the formula for π-electrons in a conjugated system: \( 4n + 2 \) (Hückel's rule) or \( 4n \), where \( n \) is an integer, to determine whether the system is aromatic or antiaromatic.

Apply the Woodward-Hoffmann rules to determine the stereochemical pathway (conrotatory or disrotatory). For photochemical conditions, if the system has \( 4n \) π-electrons, the reaction will proceed via a conrotatory pathway. If the system has \( 4n + 2 \) π-electrons, the reaction will proceed via a disrotatory pathway.

Analyze the stereochemical outcome of the ring closure. In a conrotatory pathway, the substituents on the terminal carbons of the π-system rotate in the same direction, leading to a specific cis or trans configuration. In a disrotatory pathway, the substituents rotate in opposite directions, leading to a different configuration.

Based on the pathway (conrotatory or disrotatory), predict whether the product will have a cis or trans configuration. For example, if the substituents on the terminal carbons are initially on the same side, a conrotatory closure will result in a cis product, while a disrotatory closure will result in a trans product.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Conrotatory vs. Disrotatory Ring Closure

Conrotatory and disrotatory are terms used to describe the stereochemical outcomes of pericyclic reactions, particularly in cycloadditions. In conrotatory closure, the substituents on the reacting ends of the molecule rotate in the same direction, while in disrotatory closure, they rotate in opposite directions. The type of closure is influenced by the symmetry properties of the molecular orbitals involved and the specific conditions, such as temperature and light.

Photochemical Conditions

Photochemical conditions refer to reactions that are initiated or driven by light, typically ultraviolet or visible light. Under these conditions, certain molecular orbitals can be excited, leading to different reaction pathways compared to thermal conditions. Understanding how light affects the electronic states of molecules is crucial for predicting the outcomes of reactions, including the stereochemistry of products formed during ring closures.

Cis and Trans Configurations

Cis and trans configurations describe the relative positioning of substituents on a cyclic or double-bonded structure. In a cis configuration, substituents are on the same side of the double bond or ring, while in a trans configuration, they are on opposite sides. The configuration can significantly influence the physical and chemical properties of the compound, including its stability and reactivity, making it essential to determine the outcome of reactions under specific conditions.

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