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

Sigmatropic Rearrangement

Organic Chemistry

16. Conjugated Systems

Sigmatropic Rearrangement

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1:35 minutes

Problem 18b

Textbook Question

b. Will thermal 1,5-migrations of carbon occur with retention or inversion of configuration?

Verified step by step guidance

Understand the concept of thermal 1,5-migrations: These are pericyclic reactions where a substituent migrates from one position to another within a molecule, typically involving a cyclic transition state. The reaction is governed by orbital symmetry rules (Woodward-Hoffmann rules).

Determine the stereochemical outcome: The stereochemistry of the migrating group depends on whether the reaction proceeds via a suprafacial or antarafacial pathway. Suprafacial migration occurs on the same face of the molecule, while antarafacial migration occurs on opposite faces.

Apply the Woodward-Hoffmann rules: For thermal pericyclic reactions, the reaction pathway is determined by the number of electrons involved. In a 1,5-migration, the reaction typically involves a [3,3]-sigmatropic rearrangement, which is suprafacial for thermal conditions.

Analyze the configuration of the migrating group: In a suprafacial pathway, the migrating group retains its original stereochemical configuration because it moves on the same face of the molecule during the rearrangement.

Conclude the stereochemical outcome: Based on the suprafacial nature of the thermal 1,5-migration, the reaction will occur with retention of configuration for the migrating carbon group.

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Key Concepts

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

1,5-Migration in Organic Chemistry

1,5-Migration refers to the rearrangement of a substituent from one carbon atom to another that is five positions away in a molecule. This process often occurs in the context of rearrangements involving carbocations or radical intermediates. Understanding the mechanism of 1,5-migrations is crucial for predicting the outcome of reactions involving these types of intermediates.

Retention vs. Inversion of Configuration

Retention and inversion of configuration describe how the spatial arrangement of atoms around a chiral center changes during a reaction. Retention means that the configuration remains the same, while inversion indicates that it has changed to the opposite configuration. The outcome depends on the mechanism of the reaction, particularly whether it proceeds through a planar intermediate or involves a direct bond-breaking and bond-forming process.

Thermal vs. Photochemical Reactions

Thermal reactions occur at elevated temperatures and typically involve the breaking and forming of bonds through heat energy, while photochemical reactions are driven by light energy. The conditions under which a reaction occurs can significantly influence the mechanism and stereochemical outcomes, including whether a migration leads to retention or inversion of configuration. Understanding these differences is essential for predicting reaction pathways in organic chemistry.

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Related Practice

Textbook Question

b. Using arrows, show the electron rearrangement that takes place in each reaction.

Textbook Question

Why was a deuterated compound used in the last reaction on the preceding page?

Textbook Question

Draw the product of each of the following reactions:

Textbook Question

Explain why [1,3] sigmatropic migrations of hydrogen cannot occur under thermal conditions, but [1,3] sigmatropic migrations of carbon can.

Open Question

Two products are formed in the following [1,7] sigmatropic rearrangement, one due to hydrogen migration and the other to deuterium migration. Show the configuration of the products by replacing A and B with the appropriate atoms (H or D).

Textbook Question

a. Name the kind of sigmatropic rearrangement that occurs in each of the following reactions.

Textbook Question

b. Using arrows, show the electron rearrangement that takes place in each reaction.

Textbook Question

A student found that heating any one of the isomers shown here resulted in scrambling of the deuterium to all three positions on the five-membered ring. Propose a mechanism to account for this observation.

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