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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4:59 minutes

Problem 32a

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)

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Step 1: Analyze the reaction conditions. The presence of NaOCH2CH3 (a strong base) and CH3CH2OH (a polar protic solvent) under heat suggests that the elimination mechanism is likely E2. E2 mechanisms are favored by strong bases and heat, and they occur in a single concerted step.

Step 2: Identify the substrate. The substrate is a secondary alkyl bromide. Secondary alkyl halides can undergo both E1 and E2 mechanisms, but the strong base and heat strongly favor E2.

Step 3: Determine the major and minor elimination products. In an E2 reaction, the base abstracts a proton from a β-carbon (a carbon adjacent to the carbon bonded to the leaving group). The major product is determined by Zaitsev's rule, which states that the more substituted alkene is favored. The minor product will be the less substituted alkene.

Step 4: Apply anti-periplanar geometry. In E2 reactions, the β-hydrogen and the leaving group (Br) must be anti-periplanar (opposite sides of the same plane). This stereoelectronic requirement influences which β-hydrogen is abstracted and thus the product distribution.

Step 5: Draw the major and minor products. The major product will be the more substituted alkene formed by elimination of a β-hydrogen from the carbon with more substituents. The minor product will be the less substituted alkene formed by elimination of a β-hydrogen from the less substituted β-carbon.

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Key Concepts

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

Elimination Reactions

Elimination reactions involve the removal of a leaving group and a hydrogen atom from adjacent carbon atoms, resulting in the formation of a double bond. The two main types of elimination mechanisms are E1 and E2. E1 is a two-step process where the leaving group departs first, forming a carbocation, followed by deprotonation. E2 is a one-step concerted mechanism where the base abstracts a proton while the leaving group exits simultaneously.

E1 vs. E2 Mechanisms

The E1 mechanism is favored in polar protic solvents and with substrates that can stabilize carbocations, such as tertiary or allylic halides. In contrast, the E2 mechanism requires a strong base and is favored in polar aprotic solvents, typically involving primary or secondary substrates. The choice between E1 and E2 can significantly affect the product distribution and reaction rate.

Regioselectivity in Elimination

Regioselectivity refers to the preference for the formation of one constitutional isomer over another in a chemical reaction. In elimination reactions, this can lead to major and minor products based on the stability of the resulting alkenes. The more substituted alkene is generally favored due to greater stability, following Zaitsev's rule, while less substituted products may form under certain conditions, such as steric hindrance or the use of bulky bases.

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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 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

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.

Textbook Question

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

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

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