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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3:09 minutes

Problem 20d

Textbook Question

Would the following nucleophiles be more likely to participate in an S_N1 or S_N2 reaction?
(d) NH₃

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: Evaluate the nucleophile's strength. Strong nucleophiles (e.g., negatively charged species like OH⁻ or CN⁻) favor Sₙ2 reactions because they can directly attack the substrate. Weak nucleophiles (e.g., neutral molecules like H₂O or ROH) are more likely to participate in Sₙ1 reactions, as they rely on the formation of a carbocation intermediate.

Step 3: Consider the substrate structure. Sₙ1 reactions are favored by substrates that can stabilize a carbocation intermediate, such as tertiary carbons or allylic/benzylic carbons. Sₙ2 reactions are favored by substrates with less steric hindrance, such as primary or methyl carbons.

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

Step 5: Apply these principles to the given nucleophile. Determine whether the nucleophile is strong or weak, the substrate's structure, and the solvent conditions to predict whether the reaction will proceed via an Sₙ1 or Sₙ2 mechanism.

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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 nucleophile to donate an electron pair to an electrophile during a chemical reaction. Stronger nucleophiles are more likely to participate in nucleophilic substitution reactions, influencing whether the reaction follows an Sₙ1 or Sₙ2 mechanism. Factors such as charge, electronegativity, and solvent can affect nucleophilicity.

Sₙ1 Mechanism

The Sₙ1 mechanism is a two-step nucleophilic substitution process where the first step involves the formation of a carbocation intermediate after the leaving group departs. This mechanism is favored by tertiary substrates and polar protic solvents, as they stabilize the carbocation. The rate of the reaction depends only on the concentration of the substrate, making it unimolecular.

Sₙ2 Mechanism

The Sₙ2 mechanism is a one-step nucleophilic substitution process where the nucleophile attacks the substrate simultaneously as the leaving group departs. This concerted mechanism requires strong nucleophiles and is favored by primary substrates and polar aprotic solvents. The reaction rate depends on both the substrate and the nucleophile, making it bimolecular.

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