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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3:11 minutes

Problem 74c,d

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

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 is influenced by factors such as charge, electronegativity, solvent effects, and steric hindrance.

Step 2: Analyze the solvent. Methanol is a polar protic solvent, meaning it can form hydrogen bonds with nucleophiles. Polar protic solvents tend to stabilize smaller, more electronegative nucleophiles through hydrogen bonding, reducing their nucleophilicity. Larger, less electronegative nucleophiles are less stabilized and thus more nucleophilic in such solvents.

Step 3: Compare H₂O and NH₃ in methanol. NH₃ (ammonia) is less electronegative than H₂O (water), meaning it holds its lone pair of electrons less tightly and is more willing to donate them. Additionally, NH₃ is less hydrogen-bonded in methanol compared to H₂O, making NH₃ the better nucleophile in this solvent.

Step 4: Compare Br⁻, Cl⁻, and I⁻ in methanol. In polar protic solvents like methanol, larger anions are better nucleophiles because they are less solvated (less stabilized by hydrogen bonding). I⁻ is the largest ion, followed by Br⁻, and then Cl⁻. Therefore, the nucleophilicity order in methanol is I⁻ > Br⁻ > Cl⁻.

Step 5: Summarize the rankings. For part (c), NH₃ is a better nucleophile than H₂O in methanol. For part (d), the nucleophilicity order in methanol is I⁻ > Br⁻ > Cl⁻. These rankings are based on the effects of the polar protic solvent and the intrinsic properties of the nucleophiles.

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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. Generally, negatively charged species are stronger nucleophiles than their neutral counterparts, and nucleophilicity can vary significantly in different solvents.

Solvent Effects

The solvent can significantly impact nucleophilicity by stabilizing or destabilizing the nucleophile. In polar protic solvents like methanol, nucleophiles are often less nucleophilic due to solvation effects, where solvent molecules surround and stabilize the nucleophile, making it less available to react. Understanding how solvents interact with nucleophiles is crucial for predicting their reactivity.

Comparative Nucleophilicity of Halides

When comparing halide ions (Br−, Cl−, I−), their nucleophilicity generally increases down the group in the periodic table due to decreasing electronegativity and increasing size. Iodide (I−) is typically the strongest nucleophile among the three, while bromide (Br−) is stronger than chloride (Cl−). This trend is important for ranking nucleophiles in reactions.

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