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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Problem 44b

Textbook Question

Without using pK_a values, pick out the least reactive (most stable) base in each pair. Explain your answer.
(b)

Verified step by step guidance

Step 1: Analyze the two bases provided in the image: one contains an oxygen atom with a negative charge (O⁻), and the other contains a sulfur atom with a negative charge (S⁻). Both are attached to a cyclopentane ring.

Step 2: Consider the periodic trends in electronegativity. Oxygen is more electronegative than sulfur, meaning it has a stronger tendency to attract electrons and stabilize the negative charge. This makes the oxygen-based base less reactive compared to sulfur.

Step 3: Evaluate the size of the atoms. Sulfur is larger than oxygen, which allows the negative charge to be spread over a larger area. This delocalization can contribute to stability, but sulfur's lower electronegativity makes it less effective at stabilizing the charge compared to oxygen.

Step 4: Consider the polarizability of the atoms. Sulfur is more polarizable due to its larger size, which can make it more reactive in certain chemical environments. Oxygen, being less polarizable, is generally more stable as a base.

Step 5: Conclude that the oxygen-based base (cyclopentanolate, O⁻) is the least reactive (most stable) base in this pair due to its higher electronegativity and better ability to stabilize the negative charge.

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Key Concepts

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

Acid-Base Stability

The stability of a base is influenced by its ability to accept protons and the stability of the resulting conjugate acid. A more stable base will have a lower tendency to react with protons, making it less reactive. Factors such as electronegativity, resonance, and inductive effects play crucial roles in determining this stability.

Resonance Effects

Resonance refers to the delocalization of electrons across multiple atoms, which can stabilize a base. If a base can distribute its negative charge over several atoms through resonance, it becomes more stable and less reactive. This is particularly important in comparing bases that can or cannot participate in resonance.

Inductive Effects

Inductive effects involve the transmission of charge through a chain of atoms in a molecule, influenced by electronegative atoms or groups. Electron-withdrawing groups can stabilize a negative charge on a base, making it less reactive. Understanding how these groups affect the stability of bases is essential for determining their reactivity.

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Related Practice

Textbook Question

The nitrogen screened in purple in Figure 4.43 is not protonated at physiological pH. Why?

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Textbook Question

Which is the most stable base in each pair?

(b) HS^– and HO^–

Textbook Question

Identify the stronger base in each pair. Explain your choice. Citing pK_a values is not an acceptable answer.

(d)

Textbook Question

Imidazole is a heteroaromatic base. Which nitrogen, a or b, is most basic?

Textbook Question

Using qualitative reasoning for the acid–base reactions shown,

(i) which is stronger, the acid or the conjugate acid?

(ii) Which side of the reaction is favored?

(iii) Would you expect a K_eqgreater than, equal to, or less than 1?

(b)

Textbook Question

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(a)

Textbook Question

Identify the most stable conjugate base in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer.

(f)

Textbook Question

Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.]

(b)

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Without using pKa values, pick out the least reactive (most stable) base in each pair. Explain your answer.(b)

Key Concepts

Acid-Base Stability

Resonance Effects

Inductive Effects

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Without using pK_a values, pick out the least reactive (most stable) base in each pair. Explain your answer.
(b)