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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4:27 minutes

Problem 55c

Textbook Question

How will the rate of each of the following S_N2 reactions change if it is carried out in a more polar solvent?
c.

Verified step by step guidance

Understand the SN2 reaction mechanism: SN2 reactions are bimolecular nucleophilic substitution reactions where the rate depends on both the concentration of the nucleophile and the substrate. The reaction occurs in a single step with a backside attack by the nucleophile, leading to the inversion of configuration at the carbon center.

Analyze the role of the solvent: Polar solvents can be classified as protic or aprotic. Protic solvents (e.g., water, alcohols) can form hydrogen bonds and stabilize the nucleophile, reducing its nucleophilicity. Aprotic solvents (e.g., acetone, DMSO) do not stabilize the nucleophile as much, allowing it to remain more reactive.

Consider the nucleophile (NH3): Ammonia (NH3) is a neutral nucleophile. In a more polar protic solvent, the nucleophile may be stabilized through hydrogen bonding, which can decrease its reactivity and slow down the SN2 reaction rate. In a polar aprotic solvent, the nucleophile remains more reactive, potentially increasing the reaction rate.

Evaluate the substrate (CH3CH2I): Ethyl iodide (CH3CH2I) is a good substrate for SN2 reactions due to the weak C-I bond and the relatively unhindered primary carbon. The substrate's reactivity is not significantly affected by the polarity of the solvent, but the solvent's effect on the nucleophile is crucial.

Conclude the impact of a more polar solvent: If the solvent is polar protic, the rate of the SN2 reaction may decrease due to stabilization of the nucleophile. If the solvent is polar aprotic, the rate may increase as the nucleophile remains more reactive. The specific change in rate depends on the type of polar solvent used.

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Key Concepts

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

SN2 Reaction Mechanism

The SN2 (substitution nucleophilic bimolecular) reaction is a type of nucleophilic substitution where the nucleophile attacks the electrophile simultaneously as the leaving group departs. This concerted mechanism results in a single transition state and is characterized by a second-order rate law, meaning the reaction rate depends on the concentration of both the nucleophile and the substrate.

Polarity of Solvents

Polar solvents have a significant dipole moment, which allows them to stabilize charged species and transition states through solvation. In SN2 reactions, a more polar solvent can stabilize the nucleophile and the leaving group, potentially increasing the reaction rate by lowering the activation energy required for the reaction to proceed.

Nucleophilicity and Solvent Effects

Nucleophilicity refers to the ability of a nucleophile to donate an electron pair to an electrophile. In polar solvents, nucleophilicity can be affected due to solvation effects; strong solvation can hinder the nucleophile's reactivity. Therefore, understanding how solvent polarity influences nucleophilicity is crucial for predicting the rate of SN2 reactions.

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Related Practice

Textbook Question

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

(c)

Textbook Question

For each pair, choose the haloalkane that would react most quickly in an S_N2 reaction.

(c)

Textbook Question

In which solvent—ethanol or diethyl ether—would the equilibrium for the following S_N2 reaction lie farther to the right?

Textbook Question

How will the rate of each of the following S_N2 reactions change if it is carried out in a more polar solvent?

Textbook Question

Show all the products, including their configurations, that are obtained from the above reaction.

Textbook Question

You were told in [SECTION 7.11] that is best to use a methyl halide or a primary alkyl halide for the reaction of an acetylide ion with an alkyl halide. Explain why this is so.

Textbook Question

Would you expect acetate ion (CH₃CO₂⁻) to be a better nucleophile in an S_N2 reaction with an alkyl halide carried out in methanol or in dimethyl sulfoxide?

Textbook Question

Draw a perspective structure or a Fischer projection for the products of the following S_N2 reactions.

(e)

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