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

1. A Review of General Chemistry

Resonance Structures

Organic Chemistry

1. A Review of General Chemistry

Resonance Structures

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3:17 minutes

Problem 17

Textbook Question

Use resonance forms to show delocalization of the negative charge in the Ruhemann's purple anion.

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Identify the location of the negative charge in the Ruhemann's purple anion. In the given structures, the negative charge is located on the oxygen atom of the carbonyl group.

Recognize that resonance involves the delocalization of electrons, particularly the negative charge, across the molecule. This can occur through the pi system of the aromatic rings and the carbonyl groups.

Begin by moving the lone pair of electrons from the negatively charged oxygen to form a double bond with the adjacent carbon, pushing the pi electrons of the existing carbonyl double bond onto the oxygen atom, creating a new resonance structure.

Continue the process of electron delocalization by moving the pi electrons from the newly formed double bond into the aromatic ring, allowing the negative charge to be distributed across the ring system. This can be repeated to show the charge delocalization through the entire conjugated system.

Draw all possible resonance structures, ensuring that each structure maintains the overall charge of the molecule and follows the rules of resonance, such as maintaining the octet rule for second-row elements and minimizing charge separation.

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Key Concepts

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

Resonance

Resonance in organic chemistry refers to the delocalization of electrons across adjacent atoms, allowing for multiple valid Lewis structures. These structures, known as resonance forms, depict the same molecule with different electron arrangements. Resonance stabilizes molecules by distributing charge and electron density, as seen in Ruhemann's purple anion, where the negative charge is spread across the molecule.

Delocalization of Charge

Delocalization of charge involves the spreading of electron density over several atoms, reducing the energy and increasing the stability of the molecule. In Ruhemann's purple anion, the negative charge is not confined to a single atom but is distributed across the structure, as shown in the resonance forms. This delocalization is crucial for understanding the stability and reactivity of the anion.

Anion Stability

Anion stability is influenced by factors such as resonance, electronegativity, and the ability to delocalize charge. In Ruhemann's purple anion, the stability is enhanced by resonance, which allows the negative charge to be shared among multiple atoms. This distribution reduces the potential energy and makes the anion less reactive, highlighting the importance of resonance in stabilizing charged species.

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Related Practice

Textbook Question

Draw all possible resonance structures for the reactive intermediates shown.

(b)

Textbook Question

Draw the important resonance contributors for both resonance-stabilized cations (in brackets) in the mechanism for acid-catalyzed hydrolysis of an amide.

Textbook Question

Draw two important resonance structures involving the lone pair on oxygen for the molecule shown. Which carbons are most likely to act as nucleophiles?

Textbook Question

Draw two important resonance structures involving the C―O π bond for the molecule shown. To which carbons would you expect a nucleophile to add?

Textbook Question

Draw all possible resonance structures for the reactive intermediates shown.

(c)

Textbook Question

Draw the resonance contributors of the cyclooctatrienyl dianion.

a. Which of the resonance contributors is the least stable?

Textbook Question

Which is longer, the carbon–oxygen single bond in a carboxylic acid or the carbon–oxygen bond in an alcohol? Why?

Textbook Question

Draw resonance contributors for the following ions: