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

8. Elimination Reactions

SN1 SN2 E1 E2 Chart (Big Daddy Flowchart)

Organic Chemistry

8. Elimination Reactions

SN1 SN2 E1 E2 Chart (Big Daddy Flowchart)

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Problem 15b

Textbook Question

Which of the following S_N2 and E2 reactions, respectively, is faster? Justify your choice.
(b)

Verified step by step guidance

Step 1: Analyze the reaction conditions for the SN2 reaction. In the first reaction, bromocyclohexane reacts with ethylamine (EtNH₂). SN2 reactions are favored by strong nucleophiles and polar aprotic solvents. Ethylamine is a strong nucleophile, and the reaction likely occurs in a polar aprotic solvent, which facilitates the SN2 mechanism.

Step 2: Consider steric hindrance in the SN2 reaction. Bromocyclohexane is a secondary alkyl halide, which is less favorable for SN2 reactions compared to primary alkyl halides due to increased steric hindrance. However, the reaction can still proceed if the nucleophile is strong enough.

Step 3: Analyze the reaction conditions for the E2 reaction. In the second reaction, bromocyclohexane reacts with lithium diethylamide (Et₂NLi), a strong base, followed by ethylamine. E2 reactions are favored by strong bases and anti-periplanar geometry between the leaving group and the β-hydrogen. Lithium diethylamide is a very strong base, which promotes the E2 elimination mechanism.

Step 4: Compare the leaving group and base strength. Bromine is a good leaving group in both reactions. However, the base strength differs significantly. Lithium diethylamide is much stronger than ethylamine, which makes the E2 reaction faster due to the increased rate of elimination.

Step 5: Justify the faster reaction. The E2 reaction is faster because it involves a stronger base (Et₂NLi) and is less affected by steric hindrance compared to the SN2 reaction. The SN2 reaction is slower due to the secondary alkyl halide and the moderate nucleophilicity of ethylamine.

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Key Concepts

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

SN2 Reactions

SN2 (substitution nucleophilic bimolecular) reactions involve a single concerted step where the nucleophile attacks the electrophile, leading to the displacement of a leaving group. The reaction rate depends on the concentration of both the nucleophile and the substrate, making it a second-order reaction. SN2 reactions are favored in primary substrates and polar aprotic solvents, resulting in inversion of configuration.

E2 Reactions

E2 (elimination bimolecular) reactions are characterized by a single concerted step where a base abstracts a proton while a leaving group departs, forming a double bond. The reaction rate is dependent on both the substrate and the base, making it second-order as well. E2 reactions typically occur with secondary and tertiary substrates and require strong bases, often leading to the formation of alkenes.

Reaction Conditions and Mechanism

The choice of reaction conditions, such as the strength of the nucleophile or base and the nature of the substrate, significantly influences the rate of SN2 and E2 reactions. For instance, strong bases favor E2 mechanisms, while good nucleophiles promote SN2 pathways. Additionally, steric hindrance and substrate structure (primary, secondary, or tertiary) play crucial roles in determining which reaction will proceed faster.

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Which of the following SN2 and E2 reactions, respectively, is faster? Justify your choice.(b)

Key Concepts

S<sub>N</sub>2 Reactions

E2 Reactions

Reaction Conditions and Mechanism

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Which of the following S_N2 and E2 reactions, respectively, is faster? Justify your choice.
(b)