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

8. Elimination Reactions

Nucleophiles and Basicity

Organic Chemistry

8. Elimination Reactions

Nucleophiles and Basicity

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2:26 minutes

Problem 68e,f

Textbook Question

Which member of each pair is a better nucleophile in methanol?
e. I⁻ or Br⁻
f. Cl⁻ or Br⁻

Verified step by step guidance

Step 1: Understand the concept of nucleophilicity. Nucleophilicity refers to the ability of a species to donate a pair of electrons to an electrophile. It depends on factors such as charge, electronegativity, solvent effects, and the size of the nucleophile.

Step 2: Consider the solvent. Methanol is a polar protic solvent, meaning it can form hydrogen bonds with nucleophiles. In polar protic solvents, larger, less electronegative ions are better nucleophiles because they are less tightly solvated and can more easily donate their electrons.

Step 3: Compare I⁻ and Br⁻. Iodide (I⁻) is larger and less electronegative than bromide (Br⁻). In a polar protic solvent like methanol, I⁻ is less solvated than Br⁻, making it a better nucleophile.

Step 4: Compare Cl⁻ and Br⁻. Chloride (Cl⁻) is smaller and more electronegative than bromide (Br⁻). In a polar protic solvent like methanol, Br⁻ is less solvated than Cl⁻, making Br⁻ a better nucleophile.

Step 5: Summarize the findings. In methanol, I⁻ is a better nucleophile than Br⁻, and Br⁻ is a better nucleophile than Cl⁻. This trend is due to the effects of solvation in a polar protic solvent.

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Key Concepts

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

Nucleophilicity

Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile, forming a chemical bond. It is influenced by factors such as charge, electronegativity, and solvent effects. In polar protic solvents like methanol, nucleophiles are often stabilized by solvation, which can affect their reactivity.

Solvent Effects

The solvent can significantly impact nucleophilicity, especially in polar protic solvents like methanol. In such solvents, nucleophiles with larger, more polarizable anions are often better nucleophiles because they are less solvated compared to smaller, more electronegative anions. This solvation effect can hinder the reactivity of nucleophiles.

Comparative Nucleophilicity

Comparative nucleophilicity involves evaluating the reactivity of different nucleophiles in a given solvent. For example, in the pairs I− vs. Br− and Cl− vs. Br−, the larger size and lower electronegativity of I− make it a better nucleophile than Br− in methanol, while Br− is generally a better nucleophile than Cl− due to similar considerations.

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Related Practice

Textbook Question

For each pair, predict the stronger nucleophile in the SN2 reaction (using an alcohol as the solvent). Explain your prediction.

c. NH₃ or PH₃

d. CH₃S^– or H₂S

Textbook Question

[FIGURE: KEY MECHANISM 7-1]

Show what happens in step 2 of the example if the solvent acts as a nucleophile (forming a bond to carbon) rather than as a base (removing a proton).

Textbook Question

a. Which is a stronger base: RO⁻ or RS⁻?

b. Which is a better nucleophile in an aqueous solution?

c. Which is a better nucleophile in DMSO?

Textbook Question

Which is a better nucleophile?

e. HO⁻ or ^-NH₂ in NH₃

f. HO⁻ or ^-NH₂ in DMSO

Textbook Question

Rank the following species in each set from best nucleophile to poorest nucleophile.

c. H₂O and NH₃ in methanol

d. Br⁻, Cl⁻, I⁻ in methanol

Textbook Question

How does the ratio of substitution product to elimination product formed from the reaction of propyl bromide with CH₃O⁻ in methanol change if the nucleophile is changed to CH₃S⁻?

Textbook Question

Which is a better nucleophile?

c. CH₃O⁻ or CH₃OH in H₂O

Textbook Question

Which is a better nucleophile?

d. CH₃O⁻ or CH₃OH in DMSO

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