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

E2 Mechanism

Organic Chemistry

8. Elimination Reactions

E2 Mechanism

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1:28 minutes

Problem 53c

Textbook Question

Suggest a mechanism for the following elimination reactions.
(c)

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Identify the type of elimination reaction (E1 or E2) based on the substrate, base, and reaction conditions. For example, if the substrate is tertiary and the reaction occurs in the presence of a weak base, it is likely an E1 mechanism. If the base is strong and the substrate is secondary or tertiary, it is likely an E2 mechanism.

For an E1 mechanism: (1) The leaving group departs first, forming a carbocation intermediate. (2) Analyze the stability of the carbocation and consider any possible rearrangements (e.g., hydride or alkyl shifts) to form a more stable carbocation. (3) A proton is removed from a β-carbon by a base, leading to the formation of a double bond.

For an E2 mechanism: (1) The base abstracts a proton from a β-carbon that is anti-periplanar to the leaving group. (2) Simultaneously, the leaving group departs, and a double bond forms between the α-carbon and the β-carbon. Ensure the geometry of the substrate allows for the anti-periplanar arrangement.

Draw the structure of the product(s) formed. For E1, consider the possibility of multiple products due to carbocation rearrangements or regioselectivity (Zaitsev's rule: the more substituted alkene is favored). For E2, the product is typically determined by the anti-periplanar geometry and Zaitsev's rule.

Verify the stereochemistry and regiochemistry of the product(s). For E2, ensure the anti-periplanar geometry is satisfied. For E1, check for the most stable alkene product. If multiple products are possible, indicate the major and minor products based on stability.

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Key Concepts

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

Elimination Reactions

Elimination reactions are a type of organic reaction where two substituents are removed from a molecule, resulting in the formation of a double bond or a triple bond. These reactions typically involve the loss of a small molecule, such as water or hydrogen halide, and can occur via different mechanisms, primarily E1 and E2. Understanding the conditions and substrates that favor each mechanism is crucial for predicting the outcome of elimination reactions.

E1 and E2 Mechanisms

The E1 mechanism is a two-step process involving the formation of a carbocation intermediate, followed by deprotonation to form the alkene. In contrast, the E2 mechanism is a one-step process where the base abstracts a proton while the leaving group departs, leading to the simultaneous formation of the double bond. The choice between E1 and E2 depends on factors such as substrate structure, the strength of the base, and the reaction conditions.

Regioselectivity and Stereoselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. Stereoselectivity, on the other hand, involves the preference for the formation of one stereoisomer over another. In elimination reactions, these concepts are important as they influence the final product distribution, often determined by the stability of the intermediates and the sterics of the reacting species.

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