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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3:25 minutes

Problem 45c

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)

Verified step by step guidance

Identify the structure of the given carbocation. Determine whether it is a primary, secondary, or tertiary carbocation, as this will influence its stability and likelihood of rearrangement.

Recall the concept of carbocation rearrangement: Carbocations can undergo hydride shifts or alkyl shifts to form a more stable carbocation. Stability increases in the order: primary < secondary < tertiary < allylic < benzylic.

Examine the neighboring carbon atoms to the carbocation. Check if a hydride (H⁻) or an alkyl group (R⁻) can shift to the carbocation center to form a more stable carbocation.

If a rearrangement is possible, draw the structure of the new carbocation that forms after the shift. Ensure that the new carbocation is more stable than the original.

Illustrate the mechanism of the rearrangement. Use curved arrows to show the movement of electrons during the hydride or alkyl shift, and ensure the final structure reflects the rearranged carbocation.

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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 undergo rearrangement to form more stable structures. The stability of a carbocation is influenced by factors such as the degree of substitution (primary, secondary, tertiary) and resonance. Tertiary carbocations are generally the most stable due to hyperconjugation and inductive effects from surrounding alkyl groups.

Rearrangement Mechanisms

Carbocation rearrangements typically occur through two main mechanisms: hydride shifts and alkyl shifts. A hydride shift involves the movement of a hydrogen atom with its bonding electrons to the positively charged carbon, while an alkyl shift involves the migration of an alkyl group. These shifts allow the carbocation to achieve a more stable configuration, often leading to the formation of a more substituted or resonance-stabilized carbocation.

Reaction Pathways

Understanding the reaction pathways is crucial for predicting carbocation rearrangements. The pathway includes the initial formation of the carbocation, the rearrangement step, and the final product formation. Analyzing the energy changes and intermediates involved helps in determining whether a rearrangement is favorable and what the resulting carbocation will be, guiding the drawing of the mechanism.

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Related Practice

Open Question

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

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Open Question

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

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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?

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.

(f)

Textbook Question

Which of the following carbocations would you expect to rearrange?

Textbook Question

Which of the following carbocations would you expect to undergo rearrangement?

Textbook Question

Show a reaction coordinate diagram for the two processes in Figure 13.41 that rationalizes pathway B as the one that gives the major product.

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