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

3. Acids and Bases

pKa

Organic Chemistry

3. Acids and Bases

pKa

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4:25 minutes

Problem 29c,d

Textbook Question

Arrange each group of compounds in order of increasing basicity.
c. sodium benzoate, sodium ethoxide, and sodium phenoxide
d. pyridine, sodium ethoxide, and sodium acetate

Verified step by step guidance

Step 1: Understand the concept of basicity. Basicity refers to the ability of a compound to accept protons (H⁺ ions). Strong bases are more effective at accepting protons.

Step 2: Analyze the structure of each compound in group (c). Sodium benzoate is the sodium salt of benzoic acid, sodium ethoxide is the sodium salt of ethanol, and sodium phenoxide is the sodium salt of phenol.

Step 3: Consider the electron-withdrawing or electron-donating effects of substituents in each compound in group (c). Sodium benzoate has an aromatic ring which can stabilize the negative charge, making it less basic. Sodium ethoxide is a strong base due to the alkoxide ion, and sodium phenoxide is less basic than sodium ethoxide due to resonance stabilization in the phenoxide ion.

Step 4: Analyze the structure of each compound in group (d). Pyridine is a nitrogen-containing aromatic compound, sodium ethoxide is an alkoxide ion, and sodium acetate is the sodium salt of acetic acid.

Step 5: Consider the basicity of each compound in group (d). Pyridine is a weak base due to resonance stabilization, sodium ethoxide is a strong base, and sodium acetate is less basic than sodium ethoxide due to resonance stabilization in the acetate ion.

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Key Concepts

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

Basicity in Organic Compounds

Basicity refers to the ability of a compound to accept protons (H+ ions). In organic chemistry, the basicity of a compound is influenced by the availability of lone pairs on atoms like nitrogen or oxygen, and the stability of the resulting conjugate acid. Factors such as resonance, inductive effects, and hybridization play crucial roles in determining basicity.

Resonance Stabilization

Resonance stabilization occurs when a compound can delocalize electrons across multiple atoms, reducing the availability of lone pairs for protonation and thus decreasing basicity. For example, sodium benzoate and sodium phenoxide have resonance structures that stabilize the negative charge, making them less basic compared to sodium ethoxide, which lacks such resonance.

Inductive and Electron-Withdrawing Effects

Inductive effects involve the transmission of charge through a chain of atoms, affecting basicity. Electron-withdrawing groups, like the carbonyl group in sodium acetate, decrease basicity by pulling electron density away from the atom that would accept a proton. Conversely, electron-donating groups increase basicity by enhancing electron density on the proton-accepting atom.

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Related Practice

Textbook Question

For each indicated proton, suggest an approximate pK_a value from Table 4.5. Rationalize your choice.

(d)

Textbook Question

For the bases shown, draw the conjugate acid and identify a pK_a value from Table 4.5 that would help you accurately estimate its stability.

(b)

Textbook Question

For the bases shown, draw the conjugate acid and identify a pK_a value from Table 4.5 that would help you accurately estimate its stability.

(e)

Textbook Question

Hydrogen gas (H₂) has a relatively high pK_a value. Is it a stable or unstable acid? Do you expect it to participate in acid–base reactions?

Textbook Question

Hydrogen peroxide (HOOH) has a pK_a of 11.6, making it roughly 10,000 times as strong an acid as water (pK_a = 15.7). Explain why H₂O₂ is a stronger acid than H₂O.