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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Problem 48

Textbook Question

Our wayward chemist from Assessment 8.23 suggested the following stepwise mechanism for a hydride shift. Show this mechanism on a reaction coordinate diagram to illustrate why the concerted mechanism is more likely. Justify the picture you have drawn.

Verified step by step guidance

Begin by understanding the concept of a hydride shift. A hydride shift involves the migration of a hydride ion (H⁻) from one carbon to an adjacent carbon, often to stabilize a carbocation.

Examine the provided mechanism. The first step shows a carbocation on a cyclohexane ring, with a hydride shift occurring from the adjacent carbon to stabilize the carbocation.

Consider the energy profile of the stepwise mechanism. Each step in the mechanism involves the formation of an intermediate, which typically has higher energy than the reactants or products. This can be illustrated on a reaction coordinate diagram with multiple peaks corresponding to the intermediates.

Contrast this with a concerted mechanism, where the hydride shift occurs in a single step without forming high-energy intermediates. The reaction coordinate diagram for a concerted mechanism would show a smoother transition with a single energy barrier.

Justify why the concerted mechanism is more likely. The concerted mechanism is favored because it avoids the formation of high-energy intermediates, resulting in a lower overall energy barrier and a more stable transition state.

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Key Concepts

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

Hydride Shift

A hydride shift involves the migration of a hydride ion (H-) from one carbon to an adjacent carbon, often to stabilize a carbocation. This rearrangement can lead to a more stable carbocation, facilitating subsequent reactions. Understanding hydride shifts is crucial for predicting reaction pathways and product formation in organic chemistry.

Reaction Coordinate Diagram

A reaction coordinate diagram visually represents the energy changes during a chemical reaction. It plots the progress of the reaction against the energy level, showing the transition states and intermediates. This diagram helps in comparing the energy profiles of stepwise versus concerted mechanisms, illustrating which pathway is energetically favorable.

Concerted Mechanism

A concerted mechanism involves simultaneous bond-breaking and bond-forming steps, occurring in a single transition state without intermediates. This mechanism is often favored when it results in a lower energy pathway compared to stepwise processes. Understanding concerted mechanisms is essential for predicting reaction kinetics and stability in organic transformations.

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Related Practice

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.

(a)

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.

(b)

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.

(e)

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.

(e)

Open Question

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

Molecule I

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

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