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

Substitution Comparison

Organic Chemistry

7. Substitution Reactions

Substitution Comparison

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3:32 minutes

Problem 29d

Textbook Question

Would you expect the following conditions to favor S_N1 or S_N2?
(d)

Verified step by step guidance

Step 1: Understand the difference between Sₙ1 and Sₙ2 mechanisms. Sₙ1 (unimolecular nucleophilic substitution) involves a two-step process where the leaving group departs first, forming a carbocation intermediate, followed by nucleophilic attack. Sₙ2 (bimolecular nucleophilic substitution) is a one-step process where the nucleophile attacks the substrate simultaneously as the leaving group departs.

Step 2: Analyze the substrate structure. Sₙ1 is favored by substrates that can stabilize a carbocation intermediate, such as tertiary carbons or allylic/benzylic carbons. Sₙ2 is favored by substrates with less steric hindrance, such as primary or methyl carbons.

Step 3: Consider the strength of the nucleophile. Sₙ2 is favored by strong nucleophiles because the nucleophile directly participates in the rate-determining step. Sₙ1 is less dependent on nucleophile strength since the rate-determining step is the formation of the carbocation.

Step 4: Evaluate the solvent. Polar protic solvents (e.g., water, alcohols) stabilize carbocations and favor Sₙ1. Polar aprotic solvents (e.g., acetone, DMSO) enhance the nucleophilicity of the nucleophile and favor Sₙ2.

Step 5: Assess the leaving group. A good leaving group (e.g., halides like I⁻, Br⁻, or tosylate) is essential for both Sₙ1 and Sₙ2, but it is particularly important for Sₙ1 since the leaving group departs first to form the carbocation.

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Key Concepts

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

Sₙ1 Mechanism

The Sₙ1 (substitution nucleophilic unimolecular) mechanism involves a two-step process where the leaving group departs first, forming a carbocation intermediate. This mechanism is favored in polar protic solvents and with tertiary substrates due to the stability of the carbocation. The rate of reaction depends only on the concentration of the substrate, making it unimolecular.

Sₙ2 Mechanism

The Sₙ2 (substitution nucleophilic bimolecular) mechanism is a one-step process where the nucleophile attacks the substrate simultaneously as the leaving group departs. This mechanism is favored in polar aprotic solvents and with primary substrates, as steric hindrance can impede the nucleophile's approach. The reaction rate depends on both the substrate and nucleophile concentrations, making it bimolecular.

Factors Influencing Sₙ1 vs Sₙ2

Several factors influence whether a reaction will proceed via Sₙ1 or Sₙ2 mechanisms, including substrate structure, solvent type, and the strength of the nucleophile. Tertiary substrates and polar protic solvents favor Sₙ1, while primary substrates and strong nucleophiles in polar aprotic solvents favor Sₙ2. Understanding these factors is crucial for predicting reaction pathways.

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