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

SN1 SN2 E1 E2 Chart (Big Daddy Flowchart)

Organic Chemistry

8. Elimination Reactions

SN1 SN2 E1 E2 Chart (Big Daddy Flowchart)

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4:10 minutes

Problem 23

Textbook Question

Under second-order conditions (strong base/nucleophile), S_N2 and E2 reactions may occur simultaneously and compete with each other. Show what products might be expected from the reaction of 2-bromo-3-methylbutane (a moderately hindered 2° alkyl halide) with sodium ethoxide.

Verified step by step guidance

Step 1: Identify the reaction conditions. The problem specifies second-order conditions with a strong base/nucleophile (sodium ethoxide, NaOCH₂CH₃). This indicates that both SN2 and E2 mechanisms are possible.

Step 2: Analyze the substrate. 2-bromo-3-methylbutane is a secondary (2°) alkyl halide, which is moderately hindered. This makes it suitable for both SN2 and E2 reactions, but steric hindrance may slightly favor E2 over SN2.

Step 3: Predict the SN2 product. In an SN2 reaction, the nucleophile (ethoxide ion, CH₃CH₂O⁻) will attack the carbon bonded to the bromine atom, displacing the bromine as the leaving group. The product will be an ether: 3-methyl-2-butoxyethane.

Step 4: Predict the E2 products. In an E2 reaction, the ethoxide base will abstract a β-hydrogen (a hydrogen on a carbon adjacent to the carbon bonded to the bromine). Following Zaitsev's rule, the most substituted alkene will be the major product. The major product is 2-methyl-2-butene, and the minor product is 3-methyl-1-butene.

Step 5: Summarize the competition. Both SN2 and E2 products are possible, but due to steric hindrance and the strong base/nucleophile, E2 is likely to dominate. The major E2 product is 2-methyl-2-butene, while the minor E2 product is 3-methyl-1-butene. The SN2 product (3-methyl-2-butoxyethane) may form in smaller amounts.

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Key Concepts

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

SN2 Mechanism

The SN2 mechanism is a type of nucleophilic substitution reaction where a nucleophile attacks an electrophile, resulting in the simultaneous displacement of a leaving group. This reaction occurs in a single concerted step, leading to an inversion of configuration at the carbon center. It is favored by primary and some secondary alkyl halides, especially in polar aprotic solvents, and is characterized by its dependence on steric accessibility.

E2 Mechanism

The E2 mechanism is a bimolecular elimination reaction where a strong base abstracts a proton from a β-carbon while a leaving group departs from the α-carbon, resulting in the formation of a double bond. This reaction occurs in a single concerted step and typically favors the formation of the more substituted alkene, in accordance with Zaitsev's rule. The reaction rate depends on both the base and the substrate structure, making it sensitive to steric hindrance.

Zaitsev's Rule

Zaitsev's rule states that in elimination reactions, the more substituted alkene product is favored over less substituted ones. This is due to the greater stability of more substituted alkenes, which can be attributed to hyperconjugation and the inductive effect. However, bulky bases or leaving groups can lead to exceptions, favoring the formation of less substituted alkenes, known as Hofmann products, due to steric hindrance during the elimination process.

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Related Practice

Textbook Question

Predict the products and mechanisms of the following reactions. When more than one product or mechanism is possible, explain which are most likely.

h. 1-bromo-1-methylcyclopentane heated in methanol

Textbook Question

Predict the products and mechanisms of the following reactions. When more than one product or mechanism is possible, explain which are most likely.

g. 1−bromo−1−methylcyclopentane + NaOEt in ethanol

Textbook Question

Predict the major and minor elimination products of the following proposed reactions (ignoring any possible substitutions for now). In each case, explain whether you expect the mechanism of the elimination to be E1 or E2.

(a)

Textbook Question

For each reaction, decide whether substitution or elimination (or both) is possible, and predict the products you expect. Label the major products.

a. 1−bromo−1−methylcyclohexane + NaOH in acetone

Textbook Question

When (1-bromoethyl)cyclohexane is heated in methanol for an extended period of time, five products result: two ethers and three alkenes. Predict the products of this reaction, and propose mechanisms for their formation.

Textbook Question

Give the substitution and elimination products you would expect from the following reactions.

a. 3-bromo-3-ethylpentane heated in methanol

Textbook Question

Write a balanced equation for each reaction, showing the major product you expect.

(b)

Textbook Question

If 2-fluoropentane could undergo an E1 reaction, would you expect the major product to be the more stable alkene or the less stable alkene? Explain your answer.

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Under second-order conditions (strong base/nucleophile), SN2 and E2 reactions may occur simultaneously and compete with each other. Show what products might be expected from the reaction of 2-bromo-3-methylbutane (a moderately hindered 2° alkyl halide) with sodium ethoxide.

Key Concepts

SN2 Mechanism

E2 Mechanism

Zaitsev's Rule

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Under second-order conditions (strong base/nucleophile), S_N2 and E2 reactions may occur simultaneously and compete with each other. Show what products might be expected from the reaction of 2-bromo-3-methylbutane (a moderately hindered 2° alkyl halide) with sodium ethoxide.