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

8. Elimination Reactions

Nucleophiles and Basicity

Organic Chemistry

8. Elimination Reactions

Nucleophiles and Basicity

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Problem 39c

Textbook Question

Would you expect the following bases to favor E1 or E2 elimination?
(c)

Verified step by step guidance

Step 1: Begin by identifying the base shown in the image. The base is sodium tert-butoxide (NaO-tBu), which is a strong and bulky base.

Step 2: Recall the characteristics of E1 and E2 elimination mechanisms. E1 elimination involves a carbocation intermediate and is typically favored by weak bases and polar protic solvents. E2 elimination is a concerted mechanism that requires a strong base and is influenced by steric hindrance.

Step 3: Analyze the steric hindrance of the base. Sodium tert-butoxide is a bulky base, meaning it has difficulty approaching the β-hydrogen in crowded environments. This steric hindrance makes it more likely to favor E2 elimination over E1.

Step 4: Consider the solvent and substrate. E2 elimination is favored in polar aprotic solvents and with substrates that have accessible β-hydrogens. The bulky nature of the base may also lead to preferential elimination of less sterically hindered β-hydrogens.

Step 5: Conclude that sodium tert-butoxide, due to its strong and bulky nature, will favor the E2 elimination mechanism over E1. The steric hindrance of the base plays a key role in this preference.

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Key Concepts

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

E1 and E2 Mechanisms

E1 (unimolecular elimination) and E2 (bimolecular elimination) are two types of elimination reactions in organic chemistry. E1 involves a two-step mechanism where the leaving group departs first, forming a carbocation, followed by deprotonation. In contrast, E2 is a one-step mechanism where the base abstracts a proton while the leaving group exits simultaneously, requiring a strong base and often leading to more sterically hindered substrates.

Substrate Structure

The structure of the substrate plays a crucial role in determining whether E1 or E2 mechanisms are favored. E1 reactions are more favorable with tertiary substrates due to the stability of the carbocation formed, while E2 reactions can occur with primary, secondary, or tertiary substrates, depending on the strength of the base and steric hindrance. Understanding the substrate's structure helps predict the reaction pathway.

Base Strength and Sterics

The strength and steric properties of the base influence the choice between E1 and E2 mechanisms. Strong bases favor E2 eliminations as they can effectively abstract protons in a concerted manner. Conversely, weak bases or neutral conditions may lead to E1 eliminations, especially when the substrate can stabilize a carbocation. The steric hindrance of the base also affects its ability to approach the substrate for E2 reactions.

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Textbook Question

For each pair, choose the more reactive nucleophile.

(a)

Textbook Question

In contrast to the results of Assessment 13.18, when a secondary haloalkane is treated with sodium ethanethiolate, we predict formation of a thioether. How is this rationalized?

Textbook Question

Between pyrrole and pyrrolidine, which nitrogen would be most nucleophilic? Why?

Textbook Question

The zwitterionic form of carbonyls is often used to explain their electrophilicity. Draw the zwitterionic structure of NO⁺₂. Why is this such a great electrophile at the central nitrogen?

Textbook Question

For each pair, choose the more reactive nucleophile.

(b)

Textbook Question

Would you expect methoxide ion to be a better nucleophile if it is dissolved in CH₃OH or if it is dissolved in DMSO? Why?

Textbook Question

Indicate which species in each pair gives a higher substitution-product-to-elimination-product ratio when it reacts with isopropyl bromide:

a. ethoxide ion or tert-butoxide ion

Textbook Question

For each pair, predict the stronger nucleophile in the SN2 reaction (using an alcohol as the solvent). Explain your prediction.

a. (CH₃CH₂)₃N or (CH₃CH₂)₂NH

b. (CH₃)₂O or (CH₃)₂S