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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6:26 minutes

Problem 8d

Textbook Question

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.
(d) [H₂CNO₂]^–

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Identify the structure of the nitromethane anion, \([\text{H}_2\text{CNO}_2]^−\). The central carbon atom is bonded to two hydrogen atoms and a nitro group \((\text{NO}_2)\). The nitro group is bonded to the carbon atom through a nitrogen atom.

Recognize that resonance forms involve the movement of electrons, typically through pi bonds or lone pairs. In \([\text{H}_2\text{CNO}_2]^−\), the nitro group \((\text{NO}_2)\) can exhibit resonance due to the presence of lone pairs on the oxygen atoms and the pi bond between nitrogen and oxygen.

Draw the first resonance structure: The negative charge is localized on one of the oxygen atoms, with a double bond between the nitrogen and the other oxygen atom. This is a common resonance form for nitro groups.

Draw the second resonance structure: Move the negative charge to the nitrogen atom, forming a double bond between the nitrogen and the carbon atom. This results in a single bond between nitrogen and one of the oxygen atoms, and a double bond with the other oxygen atom.

Evaluate the resonance forms: The resonance form with the negative charge on the oxygen is typically the major contributor due to oxygen's higher electronegativity compared to nitrogen. The resonance form with the negative charge on nitrogen is a minor contributor. Both forms contribute to the overall resonance hybrid, but the form with the negative charge on oxygen 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 a single Lewis structure is insufficient. The true structure is a hybrid of all possible resonance forms, contributing to the molecule's stability.

Major and Minor Contributors

In resonance, not all structures contribute equally to the resonance hybrid. Major contributors are those with the lowest energy, typically having full octets on atoms, minimal formal charges, and negative charges on more electronegative atoms. Minor contributors have higher energy due to incomplete octets, higher formal charges, or less favorable charge distributions.

Formal Charge

Formal charge is a bookkeeping tool used to determine the charge distribution within a molecule. It is calculated by subtracting the number of electrons assigned to an atom in a Lewis structure from the number of valence electrons in the free atom. Structures with formal charges closer to zero are generally more stable and are often major contributors in resonance.

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Related Practice

Textbook Question

Which of the following has delocalized electrons?

Textbook Question

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.

Textbook Question

Use resonance structures to identify the areas of high and low electron density in the following compounds:

(c)

Textbook Question

For each of these ions, draw the important resonance forms and predict which resonance form is likely to be the major contributor.

(a)

Textbook Question

Use resonance structures to identify the areas of high and low electron density in the following compounds:

(d)

Textbook Question

For each of these ions, draw the important resonance forms and predict which resonance form is likely to be the major contributor.

(b)

Textbook Question

For each of these ions, draw the important resonance forms and predict which resonance form is likely to be the major contributor.

(c)

Textbook Question

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.

(e) [CH₃C(OH)₂]⁺

(f) [CH₂CHNH]^–

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For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.(d) [H2CNO2]–

Key Concepts

Resonance Structures

Major and Minor Contributors

Formal Charge

Watch next

For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.
(d) [H₂CNO₂]^–