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

Substitution Comparison

Organic Chemistry

7. Substitution Reactions

Substitution Comparison

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2:11 minutes

Problem 27a,b

Textbook Question

For each reaction, give the expected substitution product, and predict whether the mechanism will be predominantly first order (S_N1) or second order (S_N2).
a. 2-chloro-2-methylbutane + CH₃COOH
b. isobutylbromide + sodium methoxide

Verified step by step guidance

Step 1: Analyze the substrate in each reaction to determine its structure and degree of substitution (primary, secondary, or tertiary). For reaction (a), 2-chloro-2-methylbutane is a tertiary alkyl halide, while for reaction (b), isobutylbromide is a primary alkyl halide.

Step 2: Consider the nucleophile and solvent in each reaction. For reaction (a), CH3COOH is a weak nucleophile and a polar protic solvent, which favors the SN1 mechanism. For reaction (b), sodium methoxide (CH3ONa) is a strong nucleophile and a polar aprotic solvent, which favors the SN2 mechanism.

Step 3: Predict the mechanism for each reaction based on the substrate and nucleophile/solvent combination. Reaction (a) will predominantly proceed via the SN1 mechanism due to the tertiary substrate and polar protic solvent. Reaction (b) will predominantly proceed via the SN2 mechanism due to the primary substrate and strong nucleophile in a polar aprotic solvent.

Step 4: For the substitution product, identify the nucleophile's attack site. In reaction (a), CH3COOH will replace the chlorine atom on the tertiary carbon, forming an ester. In reaction (b), sodium methoxide will replace the bromine atom on the primary carbon, forming an ether.

Step 5: Summarize the expected substitution products and mechanisms. Reaction (a) yields an ester via the SN1 mechanism, while reaction (b) yields an ether via the SN2 mechanism.

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Key Concepts

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

Nucleophilic Substitution Mechanisms

Nucleophilic substitution reactions can occur via two primary mechanisms: SN1 and SN2. SN1 reactions involve a two-step process where the leaving group departs first, forming a carbocation intermediate, followed by nucleophilic attack. In contrast, SN2 reactions are single-step processes where the nucleophile attacks the substrate simultaneously as the leaving group departs, leading to a concerted mechanism.

Factors Influencing SN1 vs. SN2

The choice between SN1 and SN2 mechanisms is influenced by several factors, including the structure of the substrate, the strength of the nucleophile, and the solvent used. Tertiary substrates favor SN1 due to stable carbocation formation, while primary substrates favor SN2 due to steric accessibility. Polar protic solvents stabilize carbocations, promoting SN1, whereas polar aprotic solvents enhance nucleophilicity, favoring SN2.

Substitution Products

The expected substitution product in nucleophilic reactions depends on the nature of the nucleophile and the substrate. For example, when a strong nucleophile reacts with a primary alkyl halide, an SN2 mechanism typically yields a single product. In contrast, with a tertiary alkyl halide and a weak nucleophile, an SN1 mechanism may lead to a racemic mixture of products due to the formation of a planar carbocation.

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Related Practice

Textbook Question

a. Optically active 2-bromobutane undergoes racemization on treatment with a solution of KBr. Give a mechanism for this racemization.

b. 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

For each reaction, give the expected substitution product, and predict whether the mechanism will be predominantly first order (SN1) or second order (SN2).

c. 1-iodo-1-methylcyclohexane + ethanol

Textbook Question

The following reaction takes place under second-order conditions (strong nucleophile), yet the structure of the product shows rearrangement. Also, the rate of this reaction is several thousand times faster than the rate of substitution of hydroxide ion on 2-chlorobutane under similar conditions. Propose a mechanism to explain the enhanced rate and rearrangement observed in this unusual reaction. (“Et” is the abbreviation for ethyl.)

Textbook Question

Using the given starting material, any necessary inorganic reagents and catalysts, and any carbon-containing compounds with no more than three carbons, indicate how each of the following compounds can be prepared:

Textbook Question

Show how you might use S_N2 reactions to convert 1-chlorobutane into the following compounds.

a. butan-1-ol

Textbook Question

Show how you might use S_N2 reactions to convert 1-chlorobutane into the following compounds.

b. 1-fluorobutane

Textbook Question

A solution of pure (S)-2-iodobutane ([α] = +15.90°) in acetone is allowed to react with radioactive iodide, ¹³¹I^–, until 1.0% of the iodobutane contains radioactive iodine. The specific rotation of this recovered iodobutane is found to be +15.58°.

b. What does this result suggest about the mechanism of the reaction of 2-iodobutane with iodide ion?

Textbook Question

Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product.

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For each reaction, give the expected substitution product, and predict whether the ­mechanism will be predominantly first order (SN1) or second order (SN2).a. 2-chloro-2-methylbutane + CH3COOHb. isobutylbromide + sodium methoxide

Key Concepts

Nucleophilic Substitution Mechanisms

Factors Influencing SN1 vs. SN2

Substitution Products

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For each reaction, give the expected substitution product, and predict whether the mechanism will be predominantly first order (S_N1) or second order (S_N2).
a. 2-chloro-2-methylbutane + CH₃COOH
b. isobutylbromide + sodium methoxide