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

E1 Reaction

Organic Chemistry

8. Elimination Reactions

E1 Reaction

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6:07 minutes

Problem 39a

Textbook Question

Propose mechanisms for the following reactions.
(a)
HINT: Alcohol dehydrations usually go through E1 elimination of the protonated alcohol, with a carbocation intermediate. Rearrangements are common.

Verified step by step guidance

Step 1: Protonation of the alcohol group - The reaction begins with the alcohol group (-OH) being protonated by phosphoric acid (H3PO4). This forms a good leaving group, water (H2O), and converts the alcohol into a protonated intermediate.

Step 2: Formation of the carbocation intermediate - After protonation, the water molecule leaves, resulting in the formation of a carbocation intermediate. This step is characteristic of an E1 elimination mechanism.

Step 3: Carbocation rearrangement (if applicable) - Check if the carbocation can undergo rearrangement to form a more stable carbocation. In this case, the carbocation is already tertiary and stable, so no rearrangement occurs.

Step 4: Elimination of a proton - A base (likely H2PO4− from the acid) abstracts a proton from a β-carbon adjacent to the carbocation. This leads to the formation of a double bond (alkene) in the product.

Step 5: Final product - The result of the elimination is the formation of cyclohexene, an alkene, as the final product.

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Key Concepts

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

E1 Mechanism

The E1 mechanism is a type of elimination reaction that involves two steps: the formation of a carbocation intermediate followed by the loss of a proton to form a double bond. This mechanism is characteristic of tertiary and some secondary alcohols, where the stability of the carbocation is crucial. The reaction rate depends only on the concentration of the substrate, making it unimolecular.

Carbocation Stability

Carbocation stability is a key factor in organic reactions, as more stable carbocations are formed preferentially. Stability increases with the degree of substitution: tertiary carbocations are more stable than secondary, which are more stable than primary. Factors such as resonance and inductive effects from adjacent groups can also enhance stability, influencing the reaction pathway.

Alcohol Dehydration

Alcohol dehydration is the process of removing a water molecule from an alcohol, typically resulting in the formation of an alkene. This reaction can occur via E1 or E2 mechanisms, with E1 being favored in acidic conditions and when heat is applied. The presence of strong acids, like phosphoric acid (H3PO4), facilitates the protonation of the alcohol, making it a better leaving group.

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