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

6. Thermodynamics and Kinetics

Carbocation Intermediate Rearrangements

Organic Chemistry

6. Thermodynamics and Kinetics

Carbocation Intermediate Rearrangements

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5:35 minutes

Problem 16a

Textbook Question

Which of the following carbocations would you expect to rearrange?

Verified step by step guidance

Step 1: Analyze the stability of each carbocation. Carbocations rearrange to achieve greater stability, typically moving from primary to secondary or secondary to tertiary carbocations.

Step 2: Examine the first carbocation (cyclopentyl carbocation). It is a secondary carbocation, and rearrangement is unlikely unless a more stable tertiary carbocation can be formed.

Step 3: Examine the second carbocation (linear structure). This is a secondary carbocation, but it is adjacent to a quaternary carbon. A hydride shift could occur to form a tertiary carbocation, which is more stable.

Step 4: Examine the third carbocation (cyclopentyl with a methyl group). This is a secondary carbocation, and rearrangement is unlikely unless a more stable tertiary carbocation can be formed.

Step 5: Examine the fourth carbocation (cyclohexyl with an isopropyl group). This is a secondary carbocation, but a hydride or alkyl shift could occur to form a tertiary carbocation, which is more stable.

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Key Concepts

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

Carbocation Stability

Carbocations are positively charged carbon species that can rearrange to form more stable structures. The stability of a carbocation is influenced by the degree of substitution: tertiary carbocations are more stable than secondary, which are more stable than primary. This stability is due to hyperconjugation and the inductive effect from surrounding alkyl groups, which help to delocalize the positive charge.

Rearrangement Mechanisms

Carbocation rearrangements typically occur through mechanisms such as hydride shifts or alkyl shifts, where a neighboring atom or group moves to stabilize the carbocation. These shifts can lead to the formation of more stable carbocations, often resulting in a change in the molecular structure. Understanding these mechanisms is crucial for predicting which carbocations will rearrange.

Ring Strain and Stability

In cyclic carbocations, ring strain can significantly affect stability and the likelihood of rearrangement. Smaller rings, such as cyclopropyl or cyclobutyl, experience more strain and are less stable than larger rings. This strain can drive rearrangements as the system seeks to relieve the strain by forming a more stable structure, often leading to the opening of the ring or the formation of a more stable carbocation.

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Related Practice

Open Question

Which of the following carbocations would be likely to rearrange? Draw each rearranged structure below.

Molecule II

Open Question

Which of the following carbocations would be likely to rearrange? Draw each rearranged structure below.

Molecule III

Open Question

Which of the following carbocations would be likely to rearrange? Draw each rearranged structure below.

Molecule IV

Textbook Question

Two of the carbocations in Problem 6-42 are prone to rearrangement. Show how they might rearrange to more stable carbocations.

Textbook Question

Which of the following carbocations would you expect to rearrange? If you expect rearrangement, draw the carbocation you expect to form and the mechanism by which it will form.

(c)

Textbook Question

Which of the following carbocations would you expect to rearrange? If you expect rearrangement, draw the carbocation you expect to form and the mechanism by which it will form.