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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4:33 minutes

Problem 33g

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

Verified step by step guidance

Step 1: Analyze the reactants. The starting material is 1-bromo-1-methylcyclopentane, which is a secondary alkyl halide. The reagent is sodium ethoxide (NaOEt) in ethanol, which is a strong base and a good nucleophile.

Step 2: Consider the possible reaction mechanisms. Since the substrate is a secondary alkyl halide and the reagent is a strong base, the reaction is likely to proceed via an E2 elimination mechanism rather than substitution (SN2 or SN1). This is because strong bases favor elimination, especially with secondary substrates.

Step 3: Identify the β-hydrogens available for elimination. In the cyclopentane ring, there are β-hydrogens on the carbons adjacent to the carbon bonded to the bromine. These hydrogens can be abstracted by the ethoxide ion during the elimination process.

Step 4: Predict the product(s). The elimination of HBr will result in the formation of a double bond in the cyclopentane ring. The most stable alkene product will be formed, following Zaitsev's rule, which states that the more substituted alkene is favored.

Step 5: Explain the stereochemistry and regioselectivity. The elimination reaction will proceed in an anti-periplanar fashion, meaning the β-hydrogen and the leaving group (Br) must be in opposite planes. This stereochemical requirement will influence the formation of the product. Additionally, the major product will be the more substituted alkene due to its greater stability.

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Key Concepts

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

Nucleophilic Substitution

Nucleophilic substitution is a fundamental reaction in organic chemistry where a nucleophile replaces a leaving group in a molecule. In this case, NaOEt acts as a nucleophile, attacking the carbon atom bonded to the bromine in 1-bromo-1-methylcyclopentane. The mechanism can proceed via either an SN1 or SN2 pathway, depending on the substrate structure and reaction conditions.

Elimination Reactions

Elimination reactions involve the removal of a small molecule (like HBr) from a larger molecule, resulting in the formation of a double bond. In the presence of a strong base like NaOEt, the reaction can favor elimination over substitution, leading to the formation of alkenes. The mechanism can be E1 or E2, with E2 being more likely in this case due to the strong base and steric hindrance.

Regioselectivity and Stereoselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others, while stereoselectivity involves the preference for one stereoisomer over another. In the reaction of 1-bromo-1-methylcyclopentane with NaOEt, the formation of products will depend on the stability of the resulting alkenes and the steric factors influencing the elimination pathway, which can lead to different regio- and stereoisomeric products.

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Related Practice

Textbook Question

Pure (S)-2-bromo-2-fluorobutane reacts with methoxide ion in methanol to give a mixture of (S)-2-fluoro-2-methoxybutane and three fluoroalkenes.

a. Use mechanisms to show which three fluoroalkenes are formed.

Textbook Question

Propose mechanisms for the following reactions. Additional products may be formed, but your mechanism only needs to explain the products shown.

(a)

Textbook Question

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

(d)

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 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

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.

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.

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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

Key Concepts

Nucleophilic Substitution

Elimination Reactions

Regioselectivity and Stereoselectivity

Watch next

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