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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Problem 23

Textbook Question

Will the following S_N2 reaction proceed more rapidly in DMSO or H₂O?

Verified step by step guidance

Step 1: Understand the reaction mechanism. The given reaction is an SN2 reaction, where the nucleophile (CN⁻) attacks the electrophilic carbon attached to the leaving group (Br⁻) in a single concerted step. SN2 reactions are bimolecular and proceed via a backside attack, leading to inversion of configuration at the carbon center.

Step 2: Analyze the role of the solvent in SN2 reactions. Polar aprotic solvents, such as DMSO (dimethyl sulfoxide), are ideal for SN2 reactions because they do not solvate the nucleophile strongly. This allows the nucleophile to remain reactive and attack the electrophilic carbon more efficiently. In contrast, polar protic solvents, such as H₂O, can hydrogen bond with the nucleophile, reducing its reactivity and slowing down the reaction.

Step 3: Evaluate the nucleophile and leaving group. In this reaction, CN⁻ is a strong nucleophile, and Br⁻ is a good leaving group. The efficiency of the nucleophile is enhanced in a polar aprotic solvent like DMSO, making the reaction proceed more rapidly.

Step 4: Consider steric factors. The substrate (2-bromopropane) is a secondary alkyl halide, which is moderately hindered. SN2 reactions are sensitive to steric hindrance, but the choice of solvent can significantly impact the reaction rate. DMSO will help minimize steric effects by enhancing nucleophilic attack.

Step 5: Conclude the solvent choice. Based on the principles of SN2 reaction mechanisms and solvent effects, the reaction will proceed more rapidly in DMSO compared to H₂O due to the increased nucleophilicity of CN⁻ in a polar aprotic environment.

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Key Concepts

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

SN2 Mechanism

The SN2 mechanism is a type of nucleophilic substitution reaction where a nucleophile attacks an electrophile, resulting in the simultaneous displacement of a leaving group. This reaction is characterized by a single concerted step, leading to an inversion of configuration at the carbon center. The rate of the reaction depends on the concentration of both the nucleophile and the substrate.

Solvent Effects

The choice of solvent can significantly influence the rate of SN2 reactions. Polar aprotic solvents, like DMSO, stabilize the nucleophile without solvation, enhancing its reactivity. In contrast, polar protic solvents, such as H2O, can solvate the nucleophile, reducing its availability to attack the substrate, thus slowing the reaction.

Nucleophilicity

Nucleophilicity refers to the strength of a nucleophile in a chemical reaction, which is influenced by factors such as charge, electronegativity, and solvent effects. Stronger nucleophiles are more reactive and can more effectively attack electrophiles. In the context of the given reaction, the nucleophile CN- from NaCN is crucial for determining the reaction rate in different solvents.

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Will the following SN2 reaction proceed more rapidly in DMSO or H2O?

Key Concepts

S<sub>N</sub>2 Mechanism

Solvent Effects

Nucleophilicity

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Will the following S_N2 reaction proceed more rapidly in DMSO or H₂O?