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: minutes

Problem 45f

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)

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 that carbocations rearrange to form more stable carbocations. Stability increases in the order: primary < secondary < tertiary < allylic < benzylic. Look for opportunities for hydride shifts or alkyl shifts that could lead to a more stable carbocation.

Examine the neighboring carbon atoms (adjacent to the carbocation). Check if a hydride (H⁻) or an alkyl group can migrate to the carbocation center to form a more stable carbocation. This is known as a 1,2-hydride shift or 1,2-alkyl shift.

Draw the structure of the rearranged carbocation. Ensure that the rearrangement follows the rules of organic chemistry, such as maintaining the correct number of bonds and observing the octet rule where applicable.

Illustrate the mechanism of the rearrangement. Use curved arrows to show the movement of electrons during the hydride or alkyl shift. Clearly label the starting carbocation, the intermediate steps (if any), and the final 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 the most stable due to hyperconjugation and inductive effects from surrounding alkyl groups, while primary carbocations are the least stable.

Carbocation Rearrangement Mechanisms

Carbocation rearrangement typically occurs through two main mechanisms: hydride shifts and alkyl shifts. In a hydride shift, a hydrogen atom from an adjacent carbon moves to the positively charged carbon, stabilizing the carbocation. An alkyl shift involves the movement of an alkyl group to the carbocation center, also leading to a more stable carbocation. Understanding these mechanisms is crucial for predicting the products of reactions involving carbocations.

Reaction Pathways and Energy Considerations

The likelihood of carbocation rearrangement is influenced by the energy of the transition states and the stability of the resulting carbocations. A reaction pathway that leads to a lower energy product is favored. When evaluating potential rearrangements, it is essential to consider the energy barriers and the stability of both the starting carbocation and the rearranged product to determine if rearrangement will occur.

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Related Practice

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?

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?

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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Textbook Question

In a strongly acidic solution, cyclohexa-1,4-diene tautomerizes to cyclohexa-1,3-diene. Propose a mechanism for this rearrangement, and explain why it is energetically favorable.

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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)

Key Concepts

Carbocation Stability

Carbocation Rearrangement Mechanisms

Reaction Pathways and Energy Considerations

Watch next

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)