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

Cumulative Substitution/Elimination

Organic Chemistry

8. Elimination Reactions

Cumulative Substitution/Elimination

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1:51 minutes

Problem 78

Textbook Question

Of the three possible elimination mechanisms (Figure 12.50), this chapter focused on two of them (E1 and E2). The third possibility occurs in situations like the one below. What makes this mechanism favored under these conditions?

Verified step by step guidance

Understand the three elimination mechanisms: E1, E2, and E1cB. E1 involves a two-step process with carbocation formation, E2 is a concerted one-step process, and E1cB involves a carbanion intermediate. The problem hints at a third mechanism, likely E1cB, so we will focus on its conditions.

Analyze the given conditions. E1cB is favored when the leaving group is poor, the β-hydrogen is acidic (due to electron-withdrawing groups nearby), and the intermediate carbanion is stabilized by resonance or inductive effects.

Examine the structure of the substrate. Look for electron-withdrawing groups (e.g., -NO₂, -CN, -COOH) near the β-carbon, which can stabilize the carbanion intermediate through resonance or inductive effects.

Consider the reaction conditions. E1cB is typically favored in basic conditions, where a strong base can deprotonate the β-hydrogen to form the carbanion intermediate.

Conclude why this mechanism is favored. The combination of a poor leaving group, a stabilized carbanion intermediate, and basic conditions makes E1cB the preferred elimination pathway under these circumstances.

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Key Concepts

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

Elimination Mechanisms

Elimination mechanisms in organic chemistry refer to the processes by which atoms or groups are removed from a molecule, resulting in the formation of a double bond. The two primary types discussed are E1 (unimolecular elimination) and E2 (bimolecular elimination), each with distinct mechanisms and conditions. Understanding these mechanisms is crucial for predicting the products of reactions and the conditions under which they occur.

E1 Mechanism

The E1 mechanism involves a two-step process where the leaving group departs first, forming a carbocation intermediate, followed by deprotonation to form a double bond. This mechanism is favored in polar protic solvents and with substrates that can stabilize the carbocation, such as tertiary alkyl halides. The rate of the reaction depends only on the concentration of the substrate, making it unimolecular.

E2 Mechanism

The E2 mechanism is a concerted process where the leaving group and a hydrogen atom are removed simultaneously, resulting in the formation of a double bond. This mechanism requires a strong base and is favored in polar aprotic solvents. The reaction rate depends on both the substrate and the base, making it bimolecular, and it typically occurs with primary or secondary substrates where steric hindrance is less of a concern.

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