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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3:26 minutes

Problem 6a,b

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?

Verified step by step guidance

Analyze the problem: The question involves the electrocyclic ring closure of a conjugated polyene under thermal conditions. This requires applying the Woodward-Hoffmann rules, which are based on the conservation of orbital symmetry.

Step 1: Determine the number of π-electrons in the system. The molecule (2E,4Z,6Z,8E)-2,4,6,8-decatetraene has four conjugated double bonds, meaning it has 4 × 2 = 8 π-electrons.

Step 2: Apply the Woodward-Hoffmann rules for thermal conditions. For a system with 4n π-electrons (where n is an integer), the ring closure will proceed via a conrotatory mechanism under thermal conditions.

Step 3: Predict the stereochemistry of the product. In a conrotatory mechanism, the terminal groups of the polyene rotate in the same direction (either both clockwise or both counterclockwise). This rotation determines whether the product will have a cis or trans configuration.

Step 4: Examine the initial stereochemistry of the molecule. The (2E,4Z,6Z,8E) configuration specifies the spatial arrangement of the substituents on the double bonds. Use this information to visualize how the conrotatory motion affects the final stereochemistry of the 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

In organic chemistry, the terms conrotatory and disrotatory refer to the specific types of stereochemical outcomes during the ring closure of conjugated systems under thermal conditions. Conrotatory closure involves both ends of the molecule rotating in the same direction, while disrotatory closure involves them rotating in opposite directions. The type of closure is determined by the number of π-bonds and the stereochemistry of the starting material.

Woodward-Hoffmann Rules

The Woodward-Hoffmann rules provide a framework for predicting the stereochemical outcomes of pericyclic reactions, including cyclizations. These rules are based on the conservation of orbital symmetry and dictate whether a reaction will proceed via a conrotatory or disrotatory mechanism, depending on the number of π-electrons involved. For a system with 4n π-electrons, the conrotatory pathway is favored, while for 4n+2 π-electrons, the disrotatory pathway is preferred.

Cis and Trans Configurations

Cis and trans configurations refer to the spatial arrangement of substituents around a double bond or a ring structure. In a cis configuration, substituents are on the same side, while in a trans configuration, they are on opposite sides. The configuration of the product formed from the ring closure of (2E,4Z,6Z,8E)-2,4,6,8-decatetraene will depend on the stereochemical pathway taken during the reaction, influencing the final spatial arrangement of the substituents.

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