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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5:41 minutes

Problem 16c,d

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

Verified step by step guidance

Understand the concept of nucleophilicity: Nucleophilicity refers to the ability of a species to donate a pair of electrons to an electrophile. In SN2 reactions, stronger nucleophiles react faster. Factors affecting nucleophilicity include charge, electronegativity, solvent effects, and the size of the nucleophile.

Analyze the solvent: The problem specifies that the solvent is an alcohol, which is a polar protic solvent. Polar protic solvents can hydrogen bond with nucleophiles, stabilizing them and reducing their nucleophilicity. Larger, less electronegative atoms are less affected by this stabilization, making them stronger nucleophiles in polar protic solvents.

Compare NH3 and PH3: Nitrogen (N) is smaller and more electronegative than phosphorus (P). In a polar protic solvent, NH3 will be more stabilized by hydrogen bonding than PH3. Since PH3 is less stabilized, it will be the stronger nucleophile in this solvent.

Compare CH3S⁻ and H2S: CH3S⁻ is negatively charged, while H2S is neutral. Negatively charged species are generally stronger nucleophiles than their neutral counterparts. Additionally, sulfur (S) is larger and less electronegative than oxygen, so CH3S⁻ will be less stabilized by the polar protic solvent compared to H2S, making CH3S⁻ the stronger nucleophile.

Summarize the predictions: For part (c), PH3 is the stronger nucleophile in an alcohol solvent. For part (d), CH3S⁻ is the stronger nucleophile due to its negative charge and reduced stabilization in the 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 during a chemical reaction. In SN2 reactions, stronger nucleophiles are typically negatively charged or have lone pairs that can readily participate in bond formation. Factors influencing nucleophilicity include charge, electronegativity, and solvent effects, with polar protic solvents often stabilizing nucleophiles and reducing their reactivity.

SN2 Mechanism

The SN2 (substitution nucleophilic bimolecular) mechanism involves a single concerted step where the nucleophile attacks the electrophile, leading to the displacement of a leaving group. This reaction is characterized by a backside attack, resulting in inversion of configuration at the carbon center. The rate of the reaction depends on the concentration of both the nucleophile and the substrate, making it bimolecular.

Solvent Effects

The choice of solvent can significantly influence the nucleophilicity of reactants in an SN2 reaction. In polar protic solvents, such as alcohols, nucleophiles can be stabilized through hydrogen bonding, which can hinder their reactivity. Conversely, polar aprotic solvents do not solvate anions as effectively, often leading to increased nucleophilicity. Understanding how solvents interact with nucleophiles is crucial for predicting reaction outcomes.