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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4:28 minutes

Problem 11

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?

Verified step by step guidance

Step 1: To determine which is a stronger base (RO⁻ or RS⁻), consider the periodic trends in electronegativity and the stability of the conjugate acid. Oxygen (O) is more electronegative than sulfur (S), meaning RO⁻ holds onto its negative charge more tightly, making it less stable and a stronger base. RS⁻, on the other hand, is more stable due to the larger size of sulfur, which can better delocalize the negative charge.

Step 2: To determine which is a better nucleophile in an aqueous solution, consider the solvation effects. In water, the smaller RO⁻ ion is more strongly solvated due to hydrogen bonding, which reduces its nucleophilicity. RS⁻, being larger and less solvated, is a better nucleophile in aqueous solution.

Step 3: To determine which is a better nucleophile in DMSO (a polar aprotic solvent), consider the lack of hydrogen bonding in such solvents. In DMSO, solvation effects are minimal, so the intrinsic nucleophilicity of the species dominates. RS⁻, being larger and more polarizable, is a better nucleophile than RO⁻ in DMSO.

Step 4: Summarize the periodic trends and solvent effects. The strength of a base is influenced by electronegativity and charge delocalization, while nucleophilicity depends on solvation and polarizability. RO⁻ is a stronger base, but RS⁻ is a better nucleophile in both aqueous and DMSO solvents.

Step 5: Conclude by emphasizing the importance of understanding the interplay between periodic trends, solvent effects, and the specific properties of the nucleophile or base in question. This knowledge is crucial for predicting reactivity in organic chemistry.

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Key Concepts

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

Basicity

Basicity refers to the ability of a species to accept protons (H+). In organic chemistry, the strength of a base is often influenced by the stability of its conjugate acid. For alkoxide ions (RO−) and thiolate ions (RS−), the presence of electronegative atoms and resonance can affect their basicity, with RO− generally being a stronger base due to the higher electronegativity of oxygen compared to sulfur.

Nucleophilicity

Nucleophilicity is the measure of a species' ability to donate an electron pair to an electrophile during a chemical reaction. Factors influencing nucleophilicity include charge, electronegativity, and solvent effects. In aqueous solutions, nucleophiles are often more hindered by solvation, while in polar aprotic solvents like DMSO, nucleophilicity can be enhanced due to reduced solvation of the nucleophile.

Solvent Effects

Solvent effects play a crucial role in determining the reactivity of nucleophiles and bases. In polar protic solvents, such as water, nucleophiles are stabilized by hydrogen bonding, which can hinder their reactivity. Conversely, in polar aprotic solvents like DMSO, nucleophiles are less solvated, allowing for greater reactivity and making them better nucleophiles in such environments.

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Related Practice

Textbook Question

Which nucleophile would be more reactive in the solvent given

(c)

Textbook Question

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

e. (CH₃)₃N or (CH₃)₂O

f. CH₃COO^– or CF₃COO^–

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

Which is a better nucleophile?

e. HO⁻ or ^-NH₂ in NH₃

f. HO⁻ or ^-NH₂ in DMSO

Textbook Question

Which member of each pair is a better nucleophile in methanol?

e. I⁻ or Br⁻

f. Cl⁻ or Br⁻

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⁻?

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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?

Key Concepts

Basicity

Nucleophilicity

Solvent Effects

Watch next

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?