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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3:27 minutes

Problem 75

Textbook Question

Which loses a proton more readily: a methyl group bonded to cyclohexane or a methyl group bonded to benzene?

Verified step by step guidance

Step 1: Analyze the structures provided in the image. Structure A shows a methyl group bonded to a benzene ring, while structure B shows a methyl group bonded to a cyclohexane ring. Benzene is aromatic, whereas cyclohexane is non-aromatic.

Step 2: Consider the acidity of the hydrogen atom attached to the methyl group in each structure. Acidity is influenced by the stability of the conjugate base formed after losing a proton. A more stable conjugate base corresponds to a more acidic proton.

Step 3: For structure A (methyl group bonded to benzene), losing a proton results in a conjugate base where the negative charge can be delocalized into the aromatic ring through resonance. This delocalization stabilizes the conjugate base.

Step 4: For structure B (methyl group bonded to cyclohexane), losing a proton results in a conjugate base where the negative charge remains localized on the carbon atom. Cyclohexane does not provide resonance stabilization, making the conjugate base less stable.

Step 5: Compare the stability of the conjugate bases. The conjugate base of structure A is more stable due to resonance stabilization in the benzene ring, making the methyl group bonded to benzene lose a proton more readily than the methyl group bonded to cyclohexane.

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Key Concepts

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

Acidity and Proton Loss

Acidity refers to the ability of a compound to donate a proton (H+). The more readily a compound loses a proton, the stronger its acidity. In organic chemistry, the stability of the resulting conjugate base after proton loss is crucial in determining acidity. Factors such as electronegativity, resonance, and hybridization play significant roles in this process.

Resonance Stabilization

Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, allowing for the delocalization of electrons. In the context of acidity, if the conjugate base formed after proton loss can be stabilized by resonance, it will be more favorable for the original compound to lose a proton. This is particularly relevant when comparing the methyl group on benzene, which benefits from resonance, to that on cyclohexane, which does not.

Inductive Effect

The inductive effect refers to the electron-withdrawing or electron-donating effects of substituents through sigma bonds. In the case of the methyl group on benzene, the presence of the aromatic ring can exert an electron-withdrawing inductive effect, which can influence the acidity of the hydrogen atom. Conversely, the cyclohexane structure does not have such electron-withdrawing characteristics, making the methyl group less acidic in that context.

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Related Practice

Textbook Question

Which acid in each of the following pairs is stronger?

Textbook Question

For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.

d. NHCH₃

e. OCH₃

f. ⁺N(CH₃)₃

Textbook Question

Explain why the pK_a of p-nitrophenol is 7.14, whereas the pK_a of m-nitrophenol is 8.39.

Textbook Question

a. Br

b. CH₂CH₃

Textbook Question

A nitro group (–NO₂) effectively stabilizes a negative charge on an adjacent carbon atom through resonance:

Two of the following nitrophenols are much more acidic than phenol itself. The third compound is only slightly more acidic than phenol. Use resonance structures of the appropriate phenoxide ions to show why two of these anions should be unusually stable.

Textbook Question

In each pair, choose the most basic compound. Justify your answer.

(d)

Textbook Question

In each pair, choose the most acidic compound. Justify your answer. The most acidic proton in each compound has been indicated.

(b)

Textbook Question

Which of the following indicated atoms would you expect to be most basic?

(c)

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