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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6:33 minutes

Problem 76

Textbook Question

a. Identify the substitution products that form when 2-bromo-2-methylpropane is dissolved in a mixture of 80% ethanol and 20% water.
b. Explain why the same products are obtained when 2-chloro-2-methylpropane is dissolved in a mixture of 80% ethanol and 20% water.

Verified step by step guidance

Step 1: Recognize that 2-bromo-2-methylpropane is a tertiary alkyl halide. Tertiary alkyl halides typically undergo substitution reactions via the SN1 mechanism in polar protic solvents like ethanol and water.

Step 2: In the SN1 mechanism, the reaction begins with the ionization of the alkyl halide. The C-Br bond breaks heterolytically, forming a carbocation (2-methyl-2-propyl carbocation) and a bromide ion (Br⁻). Write the ionization step as: \( \text{(CH}_3\text{)}_3\text{CBr} \rightarrow \text{(CH}_3\text{)}_3\text{C}^+ + \text{Br}^- \).

Step 3: The carbocation formed is stabilized by the inductive and hyperconjugative effects of the three methyl groups. The nucleophiles present in the solvent mixture (ethanol and water) can now attack the carbocation. Ethanol (\( \text{CH}_3\text{CH}_2\text{OH} \)) and water (\( \text{H}_2\text{O} \)) are both nucleophiles, and they will form substitution products by bonding to the carbocation.

Step 4: The substitution products formed are tert-butyl ethyl ether (\( \text{(CH}_3\text{)}_3\text{COCH}_2\text{CH}_3 \)) when ethanol acts as the nucleophile, and tert-butyl alcohol (\( \text{(CH}_3\text{)}_3\text{COH} \)) when water acts as the nucleophile. These are the major products of the reaction.

Step 5: For part b, the same products are obtained with 2-chloro-2-methylpropane because it is also a tertiary alkyl halide. The SN1 mechanism is favored in both cases due to the stability of the carbocation intermediate and the polar protic solvent mixture. The only difference is the leaving group (Cl⁻ vs. Br⁻), but both are good leaving groups, so the reaction proceeds similarly.

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Key Concepts

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

Nucleophilic Substitution Reactions

Nucleophilic substitution reactions involve the replacement of a leaving group in a molecule by a nucleophile. In the case of 2-bromo-2-methylpropane and 2-chloro-2-methylpropane, the nucleophile is the solvent mixture of ethanol and water. The reaction can proceed via either the SN1 or SN2 mechanism, depending on the substrate structure and reaction conditions.

SN1 vs. SN2 Mechanisms

The SN1 mechanism is a two-step process where the leaving group departs first, forming a carbocation intermediate, followed by nucleophilic attack. In contrast, the SN2 mechanism is a one-step process where the nucleophile attacks the substrate simultaneously as the leaving group departs. The structure of 2-bromo-2-methylpropane and 2-chloro-2-methylpropane favors the SN1 pathway due to steric hindrance, leading to similar products.

Solvent Effects on Reaction Pathways

The choice of solvent can significantly influence the pathway of nucleophilic substitution reactions. A polar protic solvent, like the ethanol-water mixture, stabilizes carbocations and promotes the SN1 mechanism. This stabilization allows for the formation of similar substitution products from both 2-bromo-2-methylpropane and 2-chloro-2-methylpropane, as the solvent facilitates the reaction by solvating the ions formed during the process.

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Textbook Question

When tert-butyl bromide is heated with an equal amount of ethanol in an inert solvent, one of the products is ethyl tert-butyl ether.

b. What happens to the rate if the concentration of tert-butyl bromide is tripled and the concentration of ethanol is doubled?

c. What happens to the rate if the temperature is raised?

Textbook Question

tert-Butyl chloride undergoes solvolysis in both acetic acid and formic acid. Solvolysis occurs 5000 times faster in one of these two solvents than in the other. In which solvent is solvolysis faster? Explain your answer. (Hint: Formic acid is more polar than acetic acid.)

Textbook Question

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

2-bromo-2-methylpentane, 2-chloro-2-methylpentane, 3-chloropentane, and 2-iodo-2-methylpentane.

Textbook Question

Which reaction would be faster, the one with DMSO as the solvent or the one with ethanol (EtOH)?

Textbook Question

Explain why tetrahydrofuran can solvate a positively charged species better than diethyl ether can.

Textbook Question

Two bromoethers are obtained from the reaction of the following alkyl dihalide with methanol. Draw the structures of the ethers.

Textbook Question

In contrast, optically active butan-2-ol does not racemize on treatment with a solution of KOH. Explain why a reaction like that in part (a) does not occur.

Textbook Question

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

(e) 3-chlorobut-1-ene + AgNO₃, H₂O → but-2-en-1-ol + but-3-en-2-ol

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