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 Stability

Organic Chemistry

6. Thermodynamics and Kinetics

Carbocation Stability

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4:42 minutes

Problem 28

Textbook Question

The triphenylmethyl cation is so stable that some of its salts can be stored for months. Explain why this cation is so stable.

Verified step by step guidance

The triphenylmethyl cation is stabilized by resonance. Resonance occurs when the positive charge on the central carbon atom can be delocalized across the three phenyl rings attached to it.

Each phenyl ring has a conjugated π-electron system, which allows the positive charge to be distributed over multiple atoms, reducing the overall energy of the cation.

The delocalization of the positive charge creates multiple resonance structures, which increases the stability of the molecule. This is a key feature of aromatic systems and conjugated π-electron systems.

Additionally, the phenyl rings are planar and aromatic, which further contributes to the stability of the cation through aromatic stabilization.

The combination of resonance stabilization and aromaticity makes the triphenylmethyl cation exceptionally stable, allowing its salts to be stored for extended periods.

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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 species that are classified based on their stability. Stability increases with the degree of alkyl substitution, as more alkyl groups can donate electron density through hyperconjugation and inductive effects. The triphenylmethyl cation is exceptionally stable due to resonance stabilization, where the positive charge is delocalized over multiple carbon atoms.

Resonance

Resonance is a concept in organic chemistry where a molecule can be represented by two or more valid Lewis structures, known as resonance structures. In the case of the triphenylmethyl cation, the positive charge can be delocalized across the aromatic rings, allowing for multiple resonance forms. This delocalization lowers the energy of the cation, contributing to its overall stability.

Aromaticity

Aromaticity refers to the enhanced stability of cyclic compounds with conjugated pi electron systems that follow Hückel's rule (4n + 2 pi electrons). The tropylium ion, a related structure, is aromatic and contributes to the stability of the triphenylmethyl cation. The presence of aromatic rings in the structure allows for effective electron delocalization, further stabilizing the cation.

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