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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1:24 minutes

Problem 54

Textbook Question

Amines are good nucleophiles, even though they are neutral. How would the rate of an S_N2 reaction between an amine and an alkyl halide be affected if the polarity of the solvent is increased?

Verified step by step guidance

Understand the SN2 reaction mechanism: In an SN2 reaction, the nucleophile attacks the electrophilic carbon of the alkyl halide in a single, concerted step, displacing the leaving group. The rate of the reaction depends on the strength of the nucleophile and the nature of the solvent.

Recognize the role of amines as nucleophiles: Amines are good nucleophiles because the lone pair of electrons on the nitrogen atom can readily attack the electrophilic carbon. However, their nucleophilicity can be influenced by the solvent environment.

Consider the effect of solvent polarity: In an SN2 reaction, polar aprotic solvents (e.g., acetone, DMSO) are generally preferred because they do not solvate the nucleophile strongly, allowing it to remain reactive. Polar protic solvents (e.g., water, alcohols) can hydrogen bond with the nucleophile, reducing its nucleophilicity and slowing the reaction.

Analyze the impact of increasing solvent polarity: If the polarity of the solvent is increased, and the solvent is polar protic, the amine nucleophile will be more strongly solvated through hydrogen bonding. This reduces the availability of the lone pair on nitrogen for nucleophilic attack, thereby decreasing the rate of the SN2 reaction.

Conclude the relationship: The rate of the SN2 reaction between the amine and the alkyl halide will decrease if the polarity of the solvent is increased, provided the solvent is polar protic. If the solvent is polar aprotic, the effect on the rate may be less pronounced or negligible.

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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. Amines, despite being neutral, possess a lone pair of electrons on the nitrogen atom, making them effective nucleophiles. Their nucleophilicity can be influenced by factors such as steric hindrance and the solvent environment.

SN2 Reaction Mechanism

The SN2 (substitution nucleophilic bimolecular) reaction mechanism involves a single concerted step where the nucleophile attacks the electrophile, leading to the displacement of a leaving group. This mechanism is characterized by a transition state where both the nucleophile and the substrate are involved. The rate of an SN2 reaction is dependent on the concentration of both the nucleophile and the substrate.

Solvent Polarity

Solvent polarity affects the solvation of reactants and transition states in a chemical reaction. In polar solvents, nucleophiles can be stabilized through solvation, which may reduce their reactivity. Increasing solvent polarity generally slows down SN2 reactions because it stabilizes the nucleophile, making it less available to attack the electrophile, thus decreasing the reaction rate.

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Textbook Question

Under appropriate conditions, (S)-1-bromo-1-fluoroethane reacts with sodium methoxide to give pure (S)-1-fluoro-1-methoxyethane.

a. Why is bromide rather than fluoride replaced?

b. Draw perspective structures (as shown on the previous page for 2-bromobutane) for the starting material, the transition state, and the product.

c. Does the product show retention or inversion of configuration? d. Is this result consistent with reaction by the SN2 mechanism?

Textbook Question

Which of the following S_N2 reactions should proceed at a faster rate? Justify your answer on a reaction coordinate diagram.

Textbook Question

What stereoisomers do the following reactions form?

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Write the mechanism for the reaction of a cysteine side chain with iodoacetic acid.

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

2-Acetoxycyclohexyl tosylate reacts with acetate ion to form 1,2-cyclohexanediol diacetate. The reaction is stereospecific—that is, the stereoisomers obtained as products depend on the stereoisomer used as a reactant. Recall that because 2-acetoxycyclohexyl tosylate has two asymmetric centers, it has four stereoisomers—two are cis and two are trans. Explain the following observations:

a. Both cis reactants form an optically active trans product, but each cis reactant forms a different trans product.

Textbook Question

c. A trans reactant is more reactive than a cis reactant.

Textbook Question

Which substitution reaction takes place more rapidly?

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