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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3:41 minutes

Problem 33a,b

Textbook Question

Predict the compound in each pair that will undergo the S_N2 reaction faster.
(a)
(b)

Verified step by step guidance

Step 1: Understand the SN2 reaction mechanism. SN2 reactions are bimolecular nucleophilic substitution reactions where the rate depends on both the nucleophile and the substrate. The reaction occurs in a single step with a backside attack, leading to inversion of configuration.

Step 2: Evaluate steric hindrance in the substrates. In SN2 reactions, less sterically hindered substrates react faster because the nucleophile needs access to the electrophilic carbon. Primary alkyl halides are preferred over secondary or tertiary alkyl halides.

Step 3: Analyze the leaving group. A better leaving group facilitates the SN2 reaction. Halides such as I⁻ are better leaving groups than Br⁻, which in turn are better than Cl⁻. This is due to their ability to stabilize the negative charge after leaving.

Step 4: Compare the compounds in pair (a). The first compound has a bromine attached to a tertiary carbon, which is highly sterically hindered, while the second compound has bromine attached to a primary carbon, which is less hindered. The second compound will undergo the SN2 reaction faster.

Step 5: Compare the compounds in pair (b). The first compound has chlorine as the leaving group, while the second compound has iodine. Since iodine is a better leaving group than chlorine, the second compound will undergo the SN2 reaction faster.

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

Steric Hindrance

Steric hindrance refers to the prevention of chemical reactions due to the spatial arrangement of atoms within a molecule. In SN2 reactions, steric hindrance can significantly affect the reaction rate; less hindered substrates (like primary alkyl halides) react faster than more hindered ones (like tertiary alkyl halides). This is because bulky groups around the reactive center can obstruct the nucleophile's approach.

Leaving Group Ability

The ability of a leaving group to depart from a substrate is crucial in determining the rate of SN2 reactions. Good leaving groups, such as halides (e.g., Cl-, Br-), stabilize the transition state and facilitate the reaction. The better the leaving group, the faster the reaction will proceed, as it can more readily dissociate from the substrate during the nucleophilic attack.