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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4:21 minutes

Problem 40d

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.
(d)

Verified step by step guidance

Step 1: Identify the base shown in the image. The structure represents an isopropyl anion (CH₃)₂CH⁻, which is a negatively charged carbon atom bonded to two methyl groups and one hydrogen atom.

Step 2: To draw the conjugate acid, add a proton (H⁺) to the base. This will neutralize the negative charge on the carbon atom, resulting in isopropane (CH₃)₂CH₂.

Step 3: Recall that the conjugate acid of a base has a pKₐ value that reflects its acidity. The pKₐ value can be found in Table 4.5, which lists the pKₐ values of common acids. For isopropane, the pKₐ of its conjugate acid is approximately 50, indicating it is a very weak acid.

Step 4: Use the pKₐ value to estimate the stability of the base. A high pKₐ value (like 50) suggests that the conjugate acid is very stable, and the base (isopropyl anion) is relatively unstable.

Step 5: Summarize the findings: The conjugate acid of the isopropyl anion is isopropane, and its pKₐ value of approximately 50 indicates that the base is unstable and the conjugate acid is highly stable.

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Key Concepts

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

Conjugate Acids and Bases

In acid-base chemistry, a conjugate acid is formed when a base accepts a proton (H⁺). Understanding this concept is crucial for predicting the behavior of substances in reactions. For example, when ammonia (NH₃) acts as a base, it can accept a proton to form its conjugate acid, ammonium (NH₄⁺). This relationship helps in determining the strength of acids and bases.

pKₐ and Acid Strength

pKₐ is a quantitative measure of the strength of an acid in solution, with lower values indicating stronger acids. It is derived from the acid dissociation constant (Kₐ), which reflects the extent to which an acid donates protons. Understanding pKₐ values is essential for comparing the stability of conjugate acids and bases, as they provide insight into the equilibrium position of acid-base reactions.

Stability of Conjugate Acids

The stability of a conjugate acid is influenced by factors such as electronegativity, resonance, and inductive effects. A more stable conjugate acid corresponds to a weaker base, as it is less likely to donate a proton. Evaluating the stability of conjugate acids helps in predicting the direction of acid-base reactions and understanding the relative strengths of the corresponding bases.

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Related Practice

Textbook Question

Give the pK_a value of the following compounds.

Textbook Question

Using the table of pK_a values given in [Appendix I], answer the following:

a. Which is the most acidic organic compound in the table?

b. Which is the least acidic organic compound in the table?

c. Which is the most acidic carboxylic acid in the table?

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.

(c)

Textbook Question

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

(b)

Textbook Question

a. Which is a stronger base: CH₃COO⁻ or HCOO⁻? (The pK_a of CH₃COOH is 4.8; the pK_a of HCOOH is 3.8.)

b. Which is a stronger base: HO⁻ or ^-NH₂? (The pK_a of H2O is 15.7; the pK_a of NH3 is 36.)

c. Which is a stronger base: H₂O or CH₃OH? (The pK_a of H3O+ is −1.7; the pK_a of CH₃O⁺H₂ is −2.5.)

Textbook Question

A medicinal chemist needed to deprotonate acetylene ( HC≡CH ) for use in a coupling reaction. Among the options given, which base(s) could be used for this process?

Textbook Question

For each compound, indicate the atom that is most apt to be protonated.

Textbook Question

Rank the following from strongest base to weakest base:

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