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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9:02 minutes

Problem 28b

Textbook Question

Draw the product formed when each of the following compounds undergoes an electrocyclic reaction
b. under photochemical conditions.
1.
2.

Verified step by step guidance

Step 1: Identify the type of reaction. The problem specifies an electrocyclic reaction under photochemical conditions. Electrocyclic reactions involve the conversion of a conjugated π-system into a cyclic structure or vice versa, depending on the number of π-electrons and the conditions (thermal or photochemical).

Step 2: Determine the electron count in the conjugated π-system. Both compounds shown are conjugated systems with 6 π-electrons. Under photochemical conditions, the reaction follows the Woodward-Hoffmann rules, which dictate that a 6 π-electron system undergoes a conrotatory ring closure.

Step 3: Apply the conrotatory mechanism. In a conrotatory process, the terminal groups of the conjugated system rotate in opposite directions (one clockwise and the other counterclockwise) to form the cyclic product. This rotation affects the stereochemistry of the substituents attached to the terminal carbons.

Step 4: Analyze the stereochemistry of the substituents. For the first compound, the two CH₃ groups are on opposite sides of the plane of the molecule. After conrotatory closure, the stereochemistry of the product will reflect this initial arrangement. Similarly, for the second compound, the CH₃ groups are on the same side of the plane, which will influence the stereochemistry of the cyclic product.

Step 5: Draw the cyclic product. The final product for each compound will be a cyclohexadiene structure with the substituents positioned according to the conrotatory mechanism and the initial stereochemistry of the reactants. Ensure the stereochemistry is consistent with the rules of the reaction.

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Key Concepts

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

Electrocyclic Reactions

Electrocyclic reactions are a type of pericyclic reaction where a conjugated system undergoes a cyclic transformation, typically involving the formation or breaking of sigma bonds. These reactions can be influenced by thermal or photochemical conditions, leading to different products. Understanding the mechanism and the stereochemistry involved is crucial for predicting the outcome of these reactions.

Photochemical Conditions

Photochemical conditions refer to reactions that are initiated or driven by light, particularly ultraviolet (UV) light. In electrocyclic reactions, these conditions can alter the stereochemical outcome compared to thermal conditions, often favoring the formation of different isomers. Recognizing how light energy affects molecular orbitals and reaction pathways is essential for predicting products.

Stereochemistry

Stereochemistry is the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In electrocyclic reactions, the stereochemical outcome can vary significantly depending on whether the reaction occurs under thermal or photochemical conditions. Understanding concepts like conformation and chirality is vital for accurately drawing and predicting the products of these reactions.

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