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

SN2 Reaction

Organic Chemistry

7. Substitution Reactions

SN2 Reaction

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7:43 minutes

Problem 108b

Textbook Question

The rate of the reaction of methyl iodide with quinuclidine was measured in nitrobenzene, and then the rate of the reaction of methyl iodide with triethylamine was measured in the same solvent. The concentration of the reagents was the same in both experiments.
b. The same experiment was done using isopropyl iodide instead of methyl iodide. Which reaction had the larger rate constant?

Verified step by step guidance

Step 1: Analyze the chemical structures provided. Quinuclidine (1-azabicyclo[2.2.1]hepta-2,5-diene) is a bicyclic amine with a rigid structure and a lone pair of electrons on the nitrogen atom, making it highly nucleophilic. Triisobutylamine, on the other hand, is a bulky tertiary amine with steric hindrance around the nitrogen atom, which reduces its nucleophilicity.

Step 2: Consider the reaction mechanism. The reaction of alkyl iodides with amines typically proceeds via an SN2 mechanism, where the nucleophile attacks the electrophilic carbon of the alkyl iodide, displacing the iodide ion. The rate of an SN2 reaction depends on the nucleophilicity of the amine and the steric hindrance around the electrophilic carbon.

Step 3: Compare the alkyl iodides. Methyl iodide is a small molecule with minimal steric hindrance, making it highly reactive in SN2 reactions. Isopropyl iodide, however, has increased steric hindrance due to the presence of two methyl groups attached to the electrophilic carbon, which slows down the SN2 reaction.

Step 4: Predict the effect of steric hindrance on the rate constant. Quinuclidine, being less sterically hindered and more nucleophilic, will likely react faster with both methyl iodide and isopropyl iodide compared to triisobutylamine. However, the steric hindrance of isopropyl iodide will have a greater impact on the reaction with triisobutylamine due to its already reduced nucleophilicity.

Step 5: Conclude which reaction has the larger rate constant. For isopropyl iodide, the reaction with quinuclidine will have a larger rate constant compared to the reaction with triisobutylamine, as quinuclidine is less sterically hindered and more nucleophilic, allowing it to overcome the steric hindrance of isopropyl iodide more effectively.

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Key Concepts

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

Nucleophilicity

Nucleophilicity refers to the ability of a nucleophile to donate an electron pair to an electrophile during a chemical reaction. In this context, quinuclidine and triethylamine are both nucleophiles reacting with methyl iodide and isopropyl iodide. The strength of the nucleophile affects the reaction rate, with more nucleophilic species typically leading to faster reactions.

Rate Constants and Reaction Rates

The rate constant (k) is a proportionality factor in the rate law of a reaction, indicating how quickly a reaction proceeds at a given temperature. The rate of a reaction is influenced by the nature of the reactants, solvent, and temperature. Comparing the rate constants of the reactions involving methyl iodide and isopropyl iodide helps determine which reaction is faster under the same conditions.

Solvent Effects

The choice of solvent can significantly influence the rate of a reaction by stabilizing or destabilizing reactants, intermediates, or transition states. Nitrobenzene, a polar aprotic solvent, can enhance the nucleophilicity of the nucleophiles involved in the reactions. Understanding how solvent properties affect reaction mechanisms is crucial for predicting the outcomes of the experiments described.

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Related Practice

Textbook Question

What nucleophiles would form the following compounds as a result of reacting with 1-iodobutane?

Textbook Question

Starting with an alkyl halide, how could the following compounds be prepared?

a. 2-methoxybutane

Textbook Question

Starting with an alkyl halide, how could the following compounds be prepared?

b. 1-methoxybutane

Textbook Question

2-Acetoxycyclohexyl tosylate reacts with acetate ion to form 1,2-cyclohexanediol diacetate. The reaction is stereospecific—that is, the stereoisomers obtained as products depend on the stereoisomer used as a reactant. Recall that because 2-acetoxycyclohexyl tosylate has two asymmetric centers, it has four stereoisomers—two are cis and two are trans. Explain the following observations:

b. Both trans reactants form the same racemic mixture.

Textbook Question

The rate of the reaction of methyl iodide with quinuclidine was measured in nitrobenzene, and then the rate of the reaction of methyl iodide with triethylamine was measured in the same solvent. The concentration of the reagents was the same in both experiments.

c. Which alkyl halide has the larger k_quinuclidine/k_{triethylamine} ratio?

Textbook Question

Starting with an alkyl halide, how could the following compounds be prepared?

c. butylmethylamine

Textbook Question

The reaction of an amine with an alkyl halide gives an ammonium salt.R3N amine + R'—X alkyl halide —> R3(N+)—R' X- ammonium salt The rate of this SN2 reaction is sensitive to the polarity of the solvent. 1. Draw an energy diagram for this reaction in a nonpolar solvent and another in a polar solvent. 2. Consider the nature of the transition state, and explain why this reaction should be sensitive to the polarity of the solvent. 3. Predict whether it will be faster or slower in a more polar solvent.

Textbook Question

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