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

7. Substitution Reactions

SN2 Reaction

Organic Chemistry

7. Substitution Reactions

SN2 Reaction

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3:37 minutes

Problem 57

Textbook Question

For each pair, choose the nucleophile that would react most quickly in an S_N2 reaction (assume H₂O is the solvent).
(a) F^- vs Br^-

Verified step by step guidance

Understand the Sₙ2 reaction mechanism: The Sₙ2 reaction is a bimolecular nucleophilic substitution reaction where the nucleophile attacks the electrophilic carbon in a single concerted step, leading to the inversion of configuration at the carbon center. The rate of the reaction depends on the strength of the nucleophile, steric hindrance, and the solvent.

Evaluate the nucleophiles: In an Sₙ2 reaction, a stronger nucleophile will react more quickly. Nucleophilicity is influenced by factors such as charge, electronegativity, and the ability to donate electron density. In this case, compare the two nucleophiles provided in the problem.

Consider the solvent effect: Since the solvent is H₂O (a polar protic solvent), it can stabilize anionic nucleophiles through hydrogen bonding. This stabilization reduces the nucleophilicity of anions compared to neutral species. Keep this in mind when comparing the nucleophiles.

Compare the nucleophiles based on their structure and charge: Analyze the nucleophiles in terms of their charge (anions are generally stronger nucleophiles than neutral molecules), size (smaller nucleophiles are less sterically hindered), and electronegativity (less electronegative atoms are better nucleophiles).

Choose the nucleophile that reacts most quickly: Based on the analysis, select the nucleophile that is stronger and less hindered, considering the solvent's effect on nucleophilicity. This nucleophile will react more quickly in the Sₙ2 reaction.

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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. In Sₙ2 reactions, stronger nucleophiles react more quickly because they can more effectively attack the electrophilic carbon. Factors influencing nucleophilicity include charge, electronegativity, and solvent effects, with negatively charged species generally being more nucleophilic than their neutral counterparts.

Sₙ2 Mechanism

The Sₙ2 (substitution nucleophilic bimolecular) mechanism involves a single concerted step where the nucleophile attacks the electrophile while the leaving group departs. This results in an inversion of configuration at the carbon center. The reaction rate depends on both the concentration of the nucleophile and the substrate, making it bimolecular. Sₙ2 reactions are favored by primary substrates and polar aprotic solvents.

Solvent Effects

The choice of solvent significantly impacts the rate of Sₙ2 reactions. In this case, H₂O is a polar protic solvent, which can stabilize ions but also solvate nucleophiles, potentially reducing their reactivity. Polar aprotic solvents, on the other hand, do not solvate nucleophiles as effectively, allowing them to remain more reactive. Understanding how solvent properties influence nucleophilicity is crucial for predicting reaction outcomes.

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