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

Ranking Acidity

Organic Chemistry

3. Acids and Bases

Ranking Acidity

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5:59 minutes

Problem 9

Textbook Question

Which proton, H_a or H_b, would you expect to have the lower pK_a value?

Verified step by step guidance

Step 1: Understand the relationship between pKa and acidity. The pKa value is inversely related to the acidity of a proton. A lower pKa value indicates a more acidic proton.

Step 2: Analyze the chemical environment of Hₐ and H_b. Consider factors such as electronegativity of nearby atoms, resonance stabilization, and inductive effects that can influence the acidity of each proton.

Step 3: Evaluate resonance effects. If the removal of a proton leads to a conjugate base that is resonance-stabilized, the proton is likely to be more acidic and have a lower pKa value.

Step 4: Consider inductive effects. Electronegative atoms or groups near the proton can withdraw electron density, making the proton more acidic and lowering its pKa value.

Step 5: Compare the environments of Hₐ and H_b based on the above factors to determine which proton is more acidic and thus has the lower pKa value.

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Key Concepts

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

pKₐ and Acidity

pKₐ is a measure of the acidity of a proton in a molecule, with lower pKₐ values indicating stronger acids. The pKₐ value reflects the tendency of a proton to dissociate from its parent molecule. Understanding the relationship between pKₐ and acidity is crucial for predicting which proton is more likely to be released in a chemical reaction.

Proton Position and Stability

The position of a proton in a molecule can significantly influence its acidity. Protons attached to more electronegative atoms or those that are part of a resonance-stabilized structure tend to have lower pKₐ values. Analyzing the molecular structure helps determine which proton is more stable when dissociated, thus affecting its acidity.

Resonance and Inductive Effects

Resonance and inductive effects can stabilize the conjugate base formed after a proton is lost, leading to lower pKₐ values. If the removal of a proton results in a resonance-stabilized anion or is influenced by electronegative substituents, the corresponding proton will be more acidic. Understanding these effects is essential for predicting the relative acidity of protons in different environments.

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