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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7:40 minutes

Problem 16

Textbook Question

Show how 5-methyl-1,3-cyclopentadiene rearranges to form 1-methyl-1,3-cyclopentadiene and 2-methyl-1,3-cyclopentadiene.

Verified step by step guidance

Identify the starting compound, 5-methyl-1,3-cyclopentadiene, which is a conjugated diene with a methyl group attached to the fifth carbon of the cyclopentadiene ring.

Recognize that the reaction involves a [1,5]-sigmatropic shift, a type of pericyclic reaction where a substituent (in this case, the methyl group) migrates across the conjugated π-system of the diene.

Draw the mechanism for the [1,5]-sigmatropic shift: the π-electrons of the conjugated diene rearrange, and the methyl group moves from the fifth carbon to the first carbon, forming 1-methyl-1,3-cyclopentadiene.

Consider the possibility of a second [1,5]-sigmatropic shift: the methyl group on the first carbon can migrate again across the conjugated π-system to the second carbon, forming 2-methyl-1,3-cyclopentadiene.

Verify the structures of the products (1-methyl-1,3-cyclopentadiene and 2-methyl-1,3-cyclopentadiene) to ensure that the rearrangements preserve the conjugated diene system and follow the rules of pericyclic reactions.

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Key Concepts

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

Cyclopentadiene Structure

Cyclopentadiene is a five-membered ring compound containing two double bonds. Its structure allows for unique reactivity due to the presence of conjugated double bonds, which can participate in various rearrangements and reactions. Understanding the geometry and electronic configuration of cyclopentadiene is crucial for predicting its behavior during rearrangement.

Rearrangement Mechanisms

Rearrangement mechanisms involve the reorganization of atoms within a molecule to form a new structure. In the case of 5-methyl-1,3-cyclopentadiene, the rearrangement can occur through a series of bond-breaking and bond-forming steps, often facilitated by the stability of intermediates. Recognizing the types of rearrangements, such as 1,2-shifts or ring expansions, is essential for understanding the transformation into 1-methyl-1,3-cyclopentadiene and 2-methyl-1,3-cyclopentadiene.

Stability of Intermediates

The stability of reaction intermediates plays a significant role in determining the pathway and products of a rearrangement reaction. In this case, the formation of stable carbocation or radical intermediates can influence whether the rearrangement favors the formation of 1-methyl-1,3-cyclopentadiene or 2-methyl-1,3-cyclopentadiene. Analyzing the stability of these intermediates helps predict the outcome of the rearrangement process.

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