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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2:27 minutes

Problem 58b

Textbook Question

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

Verified step by step guidance

Step 1: Recall the key factors that influence the rate of an Sₙ2 reaction. The Sₙ2 mechanism is a one-step process where the nucleophile attacks the electrophilic carbon and the leaving group departs simultaneously. The rate of the reaction depends on steric hindrance, the strength of the nucleophile, and the quality of the leaving group.

Step 2: Focus on steric hindrance. In an Sₙ2 reaction, the nucleophile must approach the electrophilic carbon from the opposite side of the leaving group. Therefore, primary haloalkanes react faster than secondary haloalkanes, and tertiary haloalkanes are generally unreactive due to steric hindrance.

Step 3: Compare the structures of the two haloalkanes in the pair. Identify whether the carbon attached to the halogen is primary, secondary, or tertiary. A primary haloalkane will react faster in an Sₙ2 reaction than a secondary haloalkane.

Step 4: Consider the leaving group. A better leaving group (e.g., I⁻ > Br⁻ > Cl⁻ > F⁻) will facilitate a faster reaction. If the two haloalkanes have different leaving groups, the one with the better leaving group will react more quickly.

Step 5: Combine your analysis of steric hindrance and leaving group quality to determine which haloalkane in the pair will react most quickly in an Sₙ2 reaction. The haloalkane with less steric hindrance and a better leaving group will be the faster-reacting compound.

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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 reaction rate, dependent on both the nucleophile and the substrate. The steric hindrance around the electrophilic carbon significantly influences the reaction rate, with less hindered substrates reacting more quickly.

Haloalkanes

Haloalkanes, or alkyl halides, are organic compounds containing carbon, hydrogen, and halogen atoms. The reactivity of haloalkanes in Sₙ2 reactions is influenced by the type of halogen and the structure of the carbon chain. Primary haloalkanes are generally more reactive than secondary or tertiary haloalkanes due to less steric hindrance, making them more accessible for nucleophilic attack.

Steric Hindrance

Steric hindrance refers to the prevention of chemical reactions due to the spatial arrangement of atoms within a molecule. In the context of Sₙ2 reactions, increased steric hindrance around the electrophilic carbon atom can slow down or inhibit the nucleophilic attack. Therefore, when comparing haloalkanes, those with less steric hindrance (such as primary haloalkanes) will typically react more quickly than those with greater steric hindrance (such as tertiary haloalkanes).

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Textbook Question

Predict the major products of the following reactions.

(a) ethyl tosylate + potassium tert-butoxide

(b) isobutyl tosylate + NaI

Textbook Question

Practice your electron-pushing skills by drawing a mechanism for the following S_N2 reactions.

(a)

Textbook Question

Practice your electron-pushing skills by drawing a mechanism for the following S_N2 reactions.

(b)

Textbook Question

Which S_N2 reaction would you expect to be faster? Explain your answer.

Textbook Question

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

(d)

Textbook Question

The following reaction, though run under standard solvolysis conditions, occurs via an S_N2 reaction. Why?

Textbook Question

Crown ethers are able to solvate cations based on their size. Specifically, 15-crown-5 forms stable complexes with sodium. How would the addition of a crown ether change the rate of an S_N2 reaction?

Textbook Question

Cardura, a drug used to treat hypertension, is synthesized as shown here.

b. Show the mechanism for conversion of A to B. Which is formed more rapidly, A or B?

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