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

Leaving Groups

Organic Chemistry

8. Elimination Reactions

Leaving Groups

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2:49 minutes

Problem 59b

Textbook Question

For each pair, choose the haloalkane that would react most quickly in an S_N1 or E1 reaction.
(b)

Verified step by step guidance

Step 1: Understand the reaction mechanism. SN1 and E1 reactions proceed via a carbocation intermediate. The stability of the carbocation formed after the leaving group departs is a key factor in determining the rate of the reaction.

Step 2: Analyze the first haloalkane (cyclohexyl iodide). When the iodine leaves, it forms a secondary carbocation. Secondary carbocations are moderately stable, but not as stable as tertiary carbocations.

Step 3: Analyze the second haloalkane (cyclohexyl iodide with a double bond and methyl group). When the iodine leaves, it forms an allylic carbocation. Allylic carbocations are stabilized by resonance, making them more stable than secondary carbocations.

Step 4: Compare the stability of the carbocations formed. The allylic carbocation formed from the second haloalkane is more stable due to resonance stabilization, which increases the rate of SN1 and E1 reactions.

Step 5: Conclude that the second haloalkane (with the double bond and methyl group) will react more quickly in an SN1 or E1 reaction because the carbocation intermediate is more stable.

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Key Concepts

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

Sₙ1 and E1 Reactions

Sₙ1 (nucleophilic substitution unimolecular) and E1 (elimination unimolecular) reactions are two types of reactions that involve a two-step mechanism. In Sₙ1 reactions, the rate-determining step is the formation of a carbocation intermediate, while in E1 reactions, the same intermediate is formed before the elimination of a leaving group. Both reactions are favored by tertiary haloalkanes due to their ability to stabilize the carbocation.

Carbocation Stability

Carbocation stability is a crucial factor in determining the rate of Sₙ1 and E1 reactions. Tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects from surrounding alkyl groups. The more stable the carbocation, the faster the reaction will proceed, making the structure of the haloalkane significant in predicting reactivity.

Leaving Group Ability

The ability of a leaving group to depart from the haloalkane is essential in both Sₙ1 and E1 reactions. Good leaving groups, such as iodide or bromide, can stabilize the transition state and facilitate the formation of the carbocation. The strength of the leaving group can significantly influence the reaction rate, with weaker bases generally being better leaving groups.

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