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 58c

Textbook Question

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

Verified step by step guidance

Step 1: Recall the key factors that influence the rate of an Sₙ2 reaction. The Sₙ2 mechanism involves a single-step nucleophilic substitution where the nucleophile attacks the electrophilic carbon and displaces the leaving group. Steric hindrance around the electrophilic carbon is a critical factor; less steric hindrance leads to faster reactions.

Step 2: Analyze the structures of the two haloalkanes. In the first compound, the chlorine atom is attached to a secondary carbon (a carbon bonded to two other carbons). In the second compound, the chlorine atom is attached to a tertiary carbon (a carbon bonded to three other carbons).

Step 3: Compare the steric hindrance around the electrophilic carbon in both compounds. The tertiary carbon in the second compound is more sterically hindered due to the presence of three alkyl groups, which makes it harder for the nucleophile to approach and react. The secondary carbon in the first compound has less steric hindrance, making it more accessible to the nucleophile.

Step 4: Recall that Sₙ2 reactions are most favorable for primary carbons, followed by secondary carbons, and least favorable for tertiary carbons due to steric hindrance. Based on this, the haloalkane with the chlorine attached to the secondary carbon will react more quickly in an Sₙ2 reaction.

Step 5: Conclude that the first compound (with the chlorine attached to the secondary carbon) will react more quickly in an Sₙ2 reaction compared to the second compound (with the chlorine attached to the tertiary carbon).

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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 the inversion of configuration at the carbon center. The rate of the Sₙ2 reaction depends on steric hindrance and the strength of the nucleophile, making primary haloalkanes more reactive than secondary or tertiary ones.

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, bulky groups around the carbon atom can impede the approach of the nucleophile, slowing down the reaction. Therefore, haloalkanes with less steric hindrance, such as primary haloalkanes, will react more quickly than those with greater steric hindrance, like tertiary haloalkanes.

Leaving Group Ability

The ability of a leaving group to depart from a molecule is crucial in determining the rate of nucleophilic substitution reactions. Good leaving groups, such as iodide or bromide, stabilize the negative charge after leaving, facilitating the reaction. In Sₙ2 reactions, the presence of a better leaving group can significantly enhance the reaction rate, making it an important factor to consider when comparing different haloalkanes.

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