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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7:44 minutes

Problem 14

Textbook Question

A carboxylic acid has two oxygen atoms, each with two nonbonding pairs of electrons.
(a) Draw the resonance forms of a carboxylic acid that is protonated on the hydroxy oxygen atom.
(b) Compare the resonance forms with those given previously for an acid protonated on the carbonyl oxygen atom.
(c) Explain why the carbonyl oxygen atom of a carboxylic acid is more basic than the hydroxy oxygen.

Verified step by step guidance

Step 1: Begin by understanding the structure of a carboxylic acid. A carboxylic acid typically has the functional group -COOH, where the carbonyl group (C=O) and the hydroxyl group (OH) are present. The oxygen atoms in these groups have lone pairs of electrons that can participate in resonance.

Step 2: For part (a), draw the resonance forms of a carboxylic acid protonated on the hydroxy oxygen atom. When the hydroxy oxygen is protonated, it forms an OH2+ group. Consider how the positive charge can be delocalized through resonance. The lone pairs on the carbonyl oxygen can shift to form a double bond with the carbon, while the existing C=O bond can shift its electrons to the oxygen, creating a resonance structure.

Step 3: For part (b), compare the resonance forms of the carboxylic acid protonated on the hydroxy oxygen with those protonated on the carbonyl oxygen. When the carbonyl oxygen is protonated, it forms a C=OH+ group. The resonance involves shifting the lone pairs from the hydroxyl oxygen to form a double bond with the carbon, while the positive charge is delocalized onto the hydroxyl oxygen. Compare the stability and delocalization of charge in both scenarios.

Step 4: For part (c), explain why the carbonyl oxygen atom is more basic than the hydroxy oxygen. Basicity is related to the ability to donate electrons. The carbonyl oxygen has a greater electron density due to resonance stabilization and is less hindered compared to the hydroxyl oxygen, which is involved in hydrogen bonding and has a more stable lone pair configuration.

Step 5: Summarize the key points: Resonance forms help in understanding the distribution of charges and electron density in protonated carboxylic acids. The carbonyl oxygen's ability to stabilize positive charge through resonance makes it more basic than the hydroxy oxygen, which is more involved in hydrogen bonding and less available for electron donation.

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Key Concepts

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

Resonance in Carboxylic Acids

Resonance involves the delocalization of electrons across adjacent atoms, stabilizing the molecule. In carboxylic acids, resonance forms show electron movement between the carbonyl and hydroxy groups. Understanding resonance helps visualize how protonation affects electron distribution and stability in different oxygen atoms.

Protonation Sites in Carboxylic Acids

Protonation refers to the addition of a proton (H+) to a molecule, affecting its structure and reactivity. In carboxylic acids, protonation can occur at either the hydroxy or carbonyl oxygen. The site of protonation influences the resonance forms and the overall stability of the molecule, crucial for comparing basicity.

Basicity of Oxygen Atoms

Basicity is the ability of an atom to accept protons. In carboxylic acids, the carbonyl oxygen is more basic than the hydroxy oxygen due to its higher electron density and resonance stabilization. This concept explains why protonation preferentially occurs at the carbonyl oxygen, affecting the molecule's reactivity and stability.

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