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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Problem 15

Textbook Question

The allylic bromide below gives two S_N1 products. Justify the formation of each.

Verified step by step guidance

Step 1: Recognize that the reaction involves an allylic bromide undergoing an SN1 mechanism. In an SN1 reaction, the rate-determining step is the formation of a carbocation intermediate after the leaving group (Br) departs.

Step 2: Identify the carbocation intermediate formed after the bromine leaves. The allylic position is stabilized by resonance, meaning the positive charge can delocalize over the π-system of the double bond. Write out the resonance structures of the carbocation to show the delocalization of charge.

Step 3: Analyze the nucleophilic attack by water (H₂O). Water can attack the carbocation at either of the two resonance-stabilized positions, leading to the formation of two different alcohol products. The attack at the less substituted position leads to the minor product, while the attack at the more substituted position leads to the major product.

Step 4: Justify the major product formation. The major product is favored because the nucleophilic attack occurs at the more substituted carbon, which is more stable due to hyperconjugation and inductive effects. This stability makes the transition state lower in energy, favoring the formation of the major product.

Step 5: Justify the minor product formation. The minor product forms because water can also attack the less substituted carbon of the carbocation intermediate. Although this pathway is less favorable, it still occurs due to the resonance stabilization of the carbocation, allowing for some distribution of products.

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Key Concepts

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

Sₙ1 Mechanism

The Sₙ1 mechanism is a type of nucleophilic substitution reaction characterized by a two-step process. In the first step, the leaving group departs, forming a carbocation intermediate. The second step involves a nucleophile attacking the carbocation, leading to the formation of the product. This mechanism typically occurs with tertiary or some secondary substrates due to the stability of the carbocation formed.

Carbocation Stability

Carbocation stability is crucial in determining the outcome of Sₙ1 reactions. Carbocations are positively charged species that can vary in stability based on their structure; tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects. The stability of the carbocation influences the rate of the reaction and the potential products formed, as more stable carbocations can lead to different nucleophilic attacks.

Regioselectivity in Nucleophilic Substitution

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others. In the context of Sₙ1 reactions, the formation of different products can occur due to the nucleophile attacking the carbocation at different positions. The regioselectivity is influenced by factors such as sterics and electronic effects, which dictate the most favorable site for nucleophilic attack on the carbocation.

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Related Practice

Textbook Question

Practice your electron-pushing skills by drawing a mechanism for the following S_N1 reactions.

(c)

Textbook Question

Provide a mechanism for the following S_N1 reactions that feature a rearrangement.

(a)

Textbook Question

Which of the following S_N1 reactions should proceed at a faster rate? Justify your answer on a reaction coordinate diagram.

Textbook Question

Practice your electron-pushing skills by drawing a mechanism for the following S_N1 reactions.

(a)

Textbook Question

Rank the ability of the following compounds to undergo an S_N1 reaction ( 1 = fastest, 5 = slowest ).

Textbook Question

Propose a mechanism for each reaction, showing explicitly how the observed mixtures of products are formed.

(b) 2-methylbut-3-en-2-ol + HBr → 1-bromo-3-methylbut-2-ene + 3-bromo-3-methylbut-1-ene

Textbook Question

Treatment of an alkyl halide with AgNO₃ in alcohol often promotes ionization.

Ag⁺ + R–Cl → AgCl + R⁺

When 4-chloro-2-methylhex-2-ene reacts with AgNO₃ in ethanol, two isomeric ethers are formed. Suggest structures, and propose a mechanism for their formation

Textbook Question

When 3-bromo-1-methylcyclohexene undergoes solvolysis in hot ethanol, two products are formed. Propose a mechanism that accounts for both of these products.

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The allylic bromide below gives two SN1 products. Justify the formation of each.

Key Concepts

Sₙ1 Mechanism

Carbocation Stability

Regioselectivity in Nucleophilic Substitution

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The allylic bromide below gives two S_N1 products. Justify the formation of each.