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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5:24 minutes

Problem 48

Textbook Question

Which reaction, E2 or Sₙ2, would you expect to be more favorable at higher temperatures?

Verified step by step guidance

Understand the key differences between E2 (bimolecular elimination) and Sₙ2 (bimolecular nucleophilic substitution) reactions. E2 reactions result in the formation of a double bond (elimination), while Sₙ2 reactions involve the substitution of a leaving group with a nucleophile.

Recall that elimination reactions, such as E2, are generally favored at higher temperatures because they lead to an increase in entropy (ΔS). The formation of a double bond and the release of a small molecule (e.g., HBr or HCl) result in more disorder in the system.

Consider the thermodynamic equation ΔG = ΔH - TΔS. At higher temperatures (T), the entropy term (TΔS) becomes more significant. Since elimination reactions have a positive ΔS, the ΔG for E2 reactions becomes more negative at higher temperatures, making them more favorable.

In contrast, Sₙ2 reactions involve a single-step substitution mechanism, which does not significantly increase entropy. Therefore, Sₙ2 reactions are less influenced by temperature compared to E2 reactions.

Conclude that E2 reactions are more favorable at higher temperatures due to the greater contribution of the entropy term (TΔS) in the Gibbs free energy equation, which drives the reaction toward elimination.

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Key Concepts

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

E2 Reaction Mechanism

The E2 (bimolecular elimination) reaction is a concerted process where a base abstracts a proton while a leaving group departs, resulting in the formation of a double bond. This mechanism typically favors more substituted alkenes and is influenced by sterics and the strength of the base. Higher temperatures can promote elimination reactions like E2 due to increased kinetic energy, which helps overcome activation barriers.

Sₙ2 Reaction Mechanism

The Sₙ2 (bimolecular nucleophilic substitution) reaction involves a nucleophile attacking an electrophile simultaneously as the leaving group departs. This mechanism is characterized by a single transition state and is favored by strong nucleophiles and less sterically hindered substrates. Higher temperatures can lead to increased reaction rates, but Sₙ2 reactions are generally more favorable at lower temperatures due to their dependence on the stability of the transition state.

Temperature Effects on Reaction Equilibria

Temperature plays a crucial role in determining the favorability of chemical reactions. According to Le Chatelier's principle, increasing temperature can shift equilibria towards endothermic processes. In the context of E2 and Sₙ2 reactions, E2 is often favored at higher temperatures because elimination reactions are typically endothermic, while Sₙ2 reactions, being more exothermic, may be less favorable under the same conditions.

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