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

Thermal Electrocyclic Reactions

Organic Chemistry

16. Conjugated Systems

Thermal Electrocyclic Reactions

Previous problemNext problem

Problem 39

Textbook Question

Explain why two different products are formed from disrotatory ring closure of (2E,4Z,6Z)-octatriene, but only one product is formed from disrotatory ring closure of (2E,4Z,6E)-octatriene.

Verified step by step guidance

Understand the concept of disrotatory ring closure: In a disrotatory ring closure, the terminal p orbitals of the conjugated system rotate in opposite directions (one clockwise and the other counterclockwise) to form a new sigma bond. The stereochemistry of the substituents on the terminal carbons determines the stereochemistry of the product.

Analyze the stereochemistry of (2E,4Z,6Z)-octatriene: The (2E,4Z,6Z) configuration means that the substituents on C2 and C6 are on opposite sides of the double bonds. This configuration allows for two possible stereochemical outcomes during the disrotatory closure, depending on the direction of rotation of the terminal p orbitals.

Explain why two products are formed for (2E,4Z,6Z)-octatriene: During the disrotatory closure, the substituents on C2 and C6 can either both end up on the same side of the newly formed ring (cis) or on opposite sides (trans). This is because the initial stereochemistry allows for two distinct ways the p orbitals can rotate to form the ring, leading to two different stereoisomers.

Analyze the stereochemistry of (2E,4Z,6E)-octatriene: The (2E,4Z,6E) configuration means that the substituents on C2 and C6 are on the same side of the double bonds. This configuration restricts the possible outcomes of the disrotatory closure, as only one stereochemical arrangement is possible due to the initial geometry of the molecule.

Explain why only one product is formed for (2E,4Z,6E)-octatriene: In this case, the disrotatory closure leads to a single stereoisomer because the substituents on C2 and C6 are already aligned in a way that only one stereochemical outcome is possible. The geometry of the molecule does not allow for the formation of a second stereoisomer.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Play a video:

Was this helpful?

Key Concepts

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

Disrotatory and Conrotatory Mechanisms

Disrotatory and conrotatory mechanisms refer to the two types of stereochemical outcomes that can occur during cyclization reactions involving conjugated systems. In disrotatory closure, the substituents on the ends of the conjugated diene rotate in opposite directions, leading to the formation of stereoisomers. Understanding these mechanisms is crucial for predicting the products of ring closures in organic reactions.

Stereochemistry of Dienes

The stereochemistry of dienes, particularly in terms of their geometric isomers (E/Z configurations), plays a significant role in determining the products of cyclization reactions. The specific arrangement of substituents around the double bonds influences the spatial orientation during the ring closure, which can lead to different stereochemical outcomes, as seen in the case of (2E,4Z,6Z)-octatriene versus (2E,4Z,6E)-octatriene.

Product Stability and Selectivity

The stability of the products formed during a reaction can greatly influence the selectivity of the reaction pathway. In the case of (2E,4Z,6Z)-octatriene, the formation of two different products suggests that both are relatively stable, allowing for their coexistence. Conversely, the formation of only one product from (2E,4Z,6E)-octatriene indicates that this product is more stable or favored, leading to a selective reaction outcome.

Watch next

Master MO Theory of Thermal Electrocyclics with a bite sized video explanation from Johnny

Start learning