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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5:00 minutes

Problem 108a

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.
a.Which reaction had the larger rate constant?

Verified step by step guidance

Step 1: Understand the problem. The question is asking which reaction has the larger rate constant when methyl iodide reacts with quinuclidine versus triethylamine in nitrobenzene, under identical concentrations.

Step 2: Recall the concept of nucleophilicity. Quinuclidine and triethylamine are both nucleophiles, but their nucleophilicity depends on factors such as steric hindrance and electronic effects. Quinuclidine is a bicyclic amine with less steric hindrance compared to triethylamine, which has bulky ethyl groups.

Step 3: Consider the solvent effect. Nitrobenzene is a polar aprotic solvent, which tends to enhance the nucleophilicity of amines by not stabilizing the nucleophile through hydrogen bonding. This means the intrinsic nucleophilicity of the amines will play a significant role in determining the rate constant.

Step 4: Relate nucleophilicity to the rate constant. In a reaction where the nucleophile attacks the electrophile (methyl iodide), a stronger nucleophile will generally lead to a faster reaction and a larger rate constant. Since quinuclidine is less sterically hindered and has a more accessible lone pair of electrons, it is likely to be a stronger nucleophile than triethylamine.

Step 5: Conclude the reasoning. Based on the steric and electronic considerations, the reaction of methyl iodide with quinuclidine is expected to have the larger rate constant compared to the reaction with triethylamine.

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Key Concepts

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

Reaction Rate and Rate Constant

The reaction rate refers to the speed at which reactants are converted into products, while the rate constant (k) is a proportionality factor in the rate law that is specific to a given reaction at a certain temperature. It reflects the intrinsic reactivity of the reactants and is influenced by factors such as the nature of the reactants and the solvent. A higher rate constant indicates a faster reaction under the same conditions.

Nucleophilicity

Nucleophilicity is a measure of how readily a nucleophile donates an electron pair to form a bond with an electrophile. In this context, quinuclidine and triethylamine are both nucleophiles reacting with methyl iodide. The strength of the nucleophile affects the reaction rate; stronger nucleophiles typically lead to faster reactions, which is crucial for determining which reaction has a larger rate constant.

Solvent Effects on Reaction Rates

The solvent can significantly influence the rate of a chemical reaction by stabilizing or destabilizing reactants, transition states, and products. Nitrobenzene, being a polar aprotic solvent, can affect the nucleophilicity of the reactants differently. Understanding how the solvent interacts with the nucleophiles and the electrophile is essential for predicting the relative rates of the reactions in question.

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