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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Problem 32

Textbook Question

What is the product of the following [1,3] sigmatropic rearrangement, A or B?

Verified step by step guidance

Step 1: Understand the concept of a [1,3] sigmatropic rearrangement. This is a pericyclic reaction where a sigma bond migrates along with the simultaneous reorganization of π-electrons. The numbers [1,3] indicate the positions of the atoms involved in the migration.

Step 2: Identify the starting material and locate the sigma bond that will migrate. Look for the bond adjacent to a π-system (such as a double bond or aromatic ring) that can participate in the rearrangement.

Step 3: Analyze the movement of electrons. Use curved arrows to show the breaking of the sigma bond and the formation of a new sigma bond at the [1,3] position. Ensure that the π-electrons are reorganized to maintain the stability of the system.

Step 4: Predict the product structure. After the rearrangement, verify the connectivity of the atoms and ensure that the new sigma bond is formed at the correct position. Compare the resulting structure to options A and B.

Step 5: Evaluate the stability of the products (A and B) if necessary. Consider factors such as resonance stabilization, steric hindrance, and electronic effects to determine which product is more likely to form.

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Key Concepts

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

[1,3] Sigmatropic Rearrangement

[1,3] sigmatropic rearrangement is a type of pericyclic reaction where a sigma bond and a pi bond undergo a concerted rearrangement. In this process, a group migrates from one atom to another within a molecule, typically involving a shift of atoms or groups across a conjugated system. Understanding the mechanism and the stereochemistry involved is crucial for predicting the product of such reactions.

Conjugation

Conjugation refers to the overlap of p-orbitals across adjacent double bonds or lone pairs, leading to increased stability and delocalization of electrons. In the context of sigmatropic rearrangements, conjugation plays a significant role in stabilizing the transition state and influencing the regioselectivity of the reaction. Recognizing the conjugated systems involved helps in determining the favored product.

Regioselectivity

Regioselectivity is the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In [1,3] sigmatropic rearrangements, the orientation of the migrating group can lead to different products, A or B. Analyzing the stability of the resulting isomers and the reaction conditions can help predict which product will be favored.

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