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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4:05 minutes

Problem 62(3)

Textbook Question

a. Draw resonance contributors for the following species, showing all the lone pairs:
b. For each species, indicate the most stable resonance contributor.
3. NO₂^-

Verified step by step guidance

Identify the structure of the NO2- ion. It consists of a nitrogen atom bonded to two oxygen atoms, with one negative charge distributed across the molecule. Nitrogen has a formal charge of -1, and the molecule has a total of 18 valence electrons (5 from nitrogen, 6 from each oxygen, and 1 extra electron for the negative charge).

Distribute the valence electrons to satisfy the octet rule for each atom. Start by placing single bonds between nitrogen and each oxygen atom, then distribute the remaining electrons as lone pairs on the oxygen atoms and nitrogen.

Draw the resonance contributors by moving electrons. In one resonance structure, one oxygen atom forms a double bond with nitrogen, while the other oxygen atom retains a single bond and carries a negative formal charge. In the second resonance structure, the double bond shifts to the other oxygen atom, and the first oxygen atom now carries the negative formal charge.

Indicate the lone pairs on all atoms in each resonance structure. Each oxygen atom should have two lone pairs when it is double-bonded to nitrogen and three lone pairs when it is single-bonded and carries the negative charge. Nitrogen will have one lone pair in both resonance structures.

Determine the most stable resonance contributor. The most stable structure is the one where the negative charge is on the more electronegative atom (oxygen). Both resonance structures are equivalent in stability because the negative charge is delocalized equally between the two oxygen atoms, making the resonance hybrid the most accurate representation of the molecule.

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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 the same molecule that depict the same arrangement of atoms but differ in the distribution of electrons. These structures help illustrate the delocalization of electrons within a molecule, which can stabilize the overall structure. In the case of NO2-, resonance contributors can be drawn to show how the negative charge and lone pairs can be distributed across the nitrogen and oxygen atoms.

Lone Pairs

Lone pairs are pairs of valence electrons that are not involved in bonding and are localized on a specific atom. In resonance structures, it is crucial to accurately represent lone pairs, as they can influence the molecule's reactivity and stability. For NO2-, the placement of lone pairs on the nitrogen and oxygen atoms will affect the resonance contributors and the overall charge distribution.

Stability of Resonance Contributors

The stability of resonance contributors is determined by factors such as the octet rule, formal charges, and the electronegativity of atoms. More stable resonance structures typically have a complete octet for all atoms, minimized formal charges, and negative charges on more electronegative atoms. Identifying the most stable resonance contributor for NO2- involves evaluating these factors to determine which structure best represents the molecule's electron distribution.

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Related Practice

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.

(g)

(h)

Textbook Question

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

Textbook Question

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

Textbook Question

Draw the resonance contributors of the cyclooctatrienyl dianion.

b. Which of the resonance contributors makes the smallest contribution to the hybrid?

Textbook Question

i) Which of the following resonance structures represents the 'actual' structure of the molecule shown? (ii) Which contributes more to the resonance hybrid? (iii) Why?

(a)

(b)

(c)

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?

10.

Textbook Question

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

Textbook Question

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

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a. Draw resonance contributors for the following species, showing all the lone pairs:b. For each species, indicate the most stable resonance contributor.3. NO2-

Key Concepts

Resonance Structures

Lone Pairs

Stability of Resonance Contributors

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a. Draw resonance contributors for the following species, showing all the lone pairs:
b. For each species, indicate the most stable resonance contributor.
3. NO₂^-