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

7. Substitution Reactions

SN1 Reaction

Organic Chemistry

7. Substitution Reactions

SN1 Reaction

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5:45 minutes

Problem 95

Textbook Question

Rank the following from most reactive to least reactive in an S_N1 reaction:

Verified step by step guidance

Step 1: Recall the mechanism of an SN1 reaction. SN1 reactions proceed via a two-step mechanism where the rate-determining step is the formation of a carbocation intermediate. The stability of the carbocation formed is the key factor in determining the reactivity of the substrate.

Step 2: Analyze the structure of compound I (2-bromobutane). When the bromine leaves, a secondary carbocation is formed. Secondary carbocations are moderately stable, but less stable than tertiary carbocations.

Step 3: Analyze the structure of compound II ((bromomethyl)benzene). When the bromine leaves, a benzyl carbocation is formed. Benzyl carbocations are highly stabilized due to resonance with the aromatic ring, making them very reactive in SN1 reactions.

Step 4: Analyze the structure of compound III ((1-bromoethyl)benzene). When the bromine leaves, a benzylic carbocation is formed, which is also stabilized by resonance with the aromatic ring. However, this carbocation is secondary, making it slightly less stable than the benzyl carbocation formed in compound II.

Step 5: Rank the compounds based on the stability of their carbocations and thus their reactivity in SN1 reactions. Compound II (benzyl carbocation) is the most reactive, followed by compound III (secondary benzylic carbocation), and finally compound I (secondary carbocation).

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Key Concepts

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

SN1 Reaction Mechanism

The SN1 (nucleophilic substitution unimolecular) reaction mechanism involves two main steps: the formation of a carbocation intermediate and the subsequent nucleophilic attack. The rate of the reaction depends solely on the concentration of the substrate, as the first step is the rate-determining step. The stability of the carbocation significantly influences the reactivity, with tertiary carbocations being more stable and reactive than secondary or primary ones.

Carbocation Stability

Carbocation stability is a crucial factor in determining the reactivity of substrates in SN1 reactions. Tertiary carbocations are the most stable due to hyperconjugation and inductive effects from surrounding alkyl groups, followed by secondary and primary carbocations. The presence of resonance, such as in benzylic or allylic carbocations, can also enhance stability, making these substrates more reactive in SN1 processes.

Substituent Effects on Reactivity

The presence of substituents on the aromatic ring or alkyl chain can significantly affect the reactivity of compounds in SN1 reactions. Electron-donating groups stabilize the carbocation, increasing reactivity, while electron-withdrawing groups can destabilize it. In the context of the provided compounds, the position of the bromine atom and the nature of the substituents will influence the overall reactivity ranking in the SN1 mechanism.

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Textbook Question

Choose the member of each pair that will react faster by the S_N1 mechanism.

a. 1-bromopropane or 2-bromopropane

b. 2-bromo-2-methylbutane or 2-bromo-3-methylbutane

Textbook Question

Furfuryl chloride can undergo substitution by both S_N2 and S_N1 mechanisms. Because it is a 1° alkyl halide, we expect S_N2 but not S_N1 reactions. Draw a mechanism for the S_N1 reaction shown below, paying careful attention to the structure of the intermediate. How can this primary halide undergo S_N1 reactions?