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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5:24 minutes

Problem 4

Textbook Question

Draw another resonance form for each of the substituted allylic cations shown in the preceding figure, showing how the positive charge is shared by another carbon atom. In each case, state whether your second resonance form is a more important or less important resonance contributor than the first structure. (Which structure places the positive charge on the more-substituted carbon atom?)

Verified step by step guidance

Identify the allylic cation structure. An allylic cation is a positively charged species where the positive charge is located on a carbon atom adjacent to a double bond.

Draw the initial resonance structure of the allylic cation. This involves showing the positive charge on the carbon atom that is directly adjacent to the double bond.

To draw another resonance form, move the electrons from the double bond towards the positively charged carbon atom. This will shift the positive charge to the other carbon atom that was part of the double bond.

Evaluate the stability of the new resonance form. The resonance form where the positive charge is on the more substituted carbon atom is generally more stable due to hyperconjugation and inductive effects.

Compare the importance of the resonance forms. The resonance form with the positive charge on the more substituted carbon atom is typically a more important contributor to the resonance hybrid because it is more stable.

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Key Concepts

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

Resonance Structures

Resonance structures are different Lewis structures for a molecule that depict the same arrangement of atoms but differ in the distribution of electrons. They are used to represent delocalized electrons within certain molecules where the bonding cannot be expressed by a single Lewis structure. Resonance structures help in understanding the stability and reactivity of the molecule.

Allylic Cations

Allylic cations are positively charged ions where the positive charge is located on a carbon atom adjacent to a carbon-carbon double bond. These cations are stabilized by resonance, as the positive charge can be delocalized over the π system of the double bond, allowing for multiple resonance structures. This delocalization increases the stability of the cation.

Substituted Carbon Atoms

In organic chemistry, a substituted carbon atom is one that is bonded to one or more substituent groups, which can affect the stability of a molecule. In the context of resonance, placing a positive charge on a more-substituted carbon atom often results in a more stable resonance structure due to hyperconjugation and inductive effects, which help to delocalize the positive charge more effectively.

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Related Practice

Textbook Question

a. Draw resonance contributors for the following species. Do not include structures that are so unstable that their contributions to the resonance hybrid would be negligible. Indicate which are major contributors and which are minor contributors to the resonance hybrid.

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

13.

Textbook Question

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

15.

Textbook Question

Which resonance contributor in each pair makes the greater contribution to the resonance hybrid?

Textbook Question

Which resonance contributor in each pair makes the greater contribution to the resonance hybrid?

Textbook Question

Draw the Lewis structure of azidomethane (CH₃N₃) [Show two important resonance structures.]

Textbook Question

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

14.

Textbook Question

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

Multiple Choice

Which is NOT a valid resonance contributor of acetamide?

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