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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3:07 minutes

Problem 57b

Textbook Question

For each pair, choose the nucleophile that would react most quickly in an S_N2 reaction (assume H₂O is the solvent).
(b)

Verified step by step guidance

Step 1: Understand the Sₙ2 reaction mechanism. Sₙ2 reactions are bimolecular nucleophilic substitution reactions where the nucleophile attacks the electrophilic carbon in a single step, leading to the displacement of the leaving group. The rate of the reaction depends on the strength of the nucleophile and steric hindrance around the electrophilic carbon.

Step 2: Evaluate the nucleophiles provided in the pair. In an Sₙ2 reaction, a stronger nucleophile will react more quickly. Nucleophilicity is influenced by factors such as charge, electronegativity, and the solvent. In this case, H₂O is the solvent, which is polar protic and can stabilize charged nucleophiles, reducing their reactivity.

Step 3: Compare the nucleophiles based on their structure and charge. A negatively charged nucleophile is generally stronger than a neutral one. Additionally, less electronegative atoms tend to be better nucleophiles because they hold their electrons less tightly and are more willing to donate them.

Step 4: Consider steric hindrance. In an Sₙ2 reaction, bulky nucleophiles are less effective because they face difficulty accessing the electrophilic carbon. Smaller, less hindered nucleophiles will react more quickly.

Step 5: Make a decision based on the above factors. Identify which nucleophile in the pair is stronger and less sterically hindered, and thus would react most quickly in the Sₙ2 reaction in the presence of H₂O as the 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. In Sₙ2 reactions, stronger nucleophiles react more quickly due to their greater electron density and ability to stabilize the transition state. 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 simultaneously displacing a leaving group. This reaction is characterized by a backside attack, leading to inversion of configuration at the chiral center. The rate of an Sₙ2 reaction depends on both the concentration of the nucleophile and the electrophile, making it bimolecular.

Solvent Effects

The choice of solvent can significantly influence the rate of Sₙ2 reactions. Polar protic solvents, like water, can stabilize ions through solvation, which may hinder nucleophilicity by surrounding the nucleophile and making it less reactive. In contrast, polar aprotic solvents do not solvate anions as effectively, allowing nucleophiles to remain more reactive. Understanding solvent effects is crucial for predicting reaction outcomes in nucleophilic substitutions.

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