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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5:32 minutes

Problem 112a

Textbook Question

Draw the major elimination product that would be obtained from each of the following reactants with a strong base and with a weak base:
a.

Verified step by step guidance

Analyze the structure: The given compound is a brominated cyclopentanone with substituents at the 2-position (Br and CH3) and 3-position (H and CH3). The bromine atom is a good leaving group, making this molecule suitable for elimination reactions.

Determine the elimination mechanism: With a strong base, the reaction typically follows the E2 mechanism, which is a one-step process requiring anti-periplanar geometry between the leaving group (Br) and the β-hydrogen. With a weak base, the reaction may proceed via the E1 mechanism, which involves a carbocation intermediate.

Identify β-hydrogens: The β-hydrogens are located on the carbon atoms adjacent to the carbon bonded to the bromine atom. In this case, the β-hydrogens are on the 3-position (attached to the carbon with the H and CH3 substituents).

Predict the major product with a strong base: For the E2 mechanism, the anti-periplanar geometry must be considered. The β-hydrogen on the same plane as the bromine will be abstracted, leading to the formation of a double bond between the 2-position and 3-position carbons. The major product will be the most stable alkene, likely the one with the methyl group contributing to hyperconjugation.

Predict the major product with a weak base: For the E1 mechanism, the bromine leaves first, forming a carbocation at the 2-position. The carbocation is stabilized by resonance with the ketone group. The β-hydrogen is then removed, forming the most substituted and stable alkene as the major product.

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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 atoms or groups from a molecule, resulting in the formation of a double bond or a ring structure. In organic chemistry, these reactions can be classified as E1 or E2, depending on the mechanism. E2 reactions typically require a strong base and occur in a single concerted step, while E1 reactions involve a two-step mechanism with a carbocation intermediate, often favored by weak bases.

Strong vs. Weak Bases

The strength of a base significantly influences the outcome of elimination reactions. Strong bases, such as sodium hydride (NaH) or potassium tert-butoxide (KOtBu), promote E2 mechanisms, leading to the formation of alkenes. In contrast, weak bases, like water or alcohols, may favor E1 mechanisms, resulting in different products due to the stability of intermediates and the reaction conditions.

Zaitsev's Rule

Zaitsev's Rule states that in elimination reactions, the more substituted alkene is typically the major product. This is due to the stability of more substituted double bonds, which are less reactive and more thermodynamically favorable. Understanding this rule helps predict the major product when analyzing elimination reactions, especially when considering the base strength and the structure of the reactants.

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Related Practice

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.

Textbook Question

Four alkenes are formed from the E1 reaction of 3-bromo-2,3-dimethylpentane and methanol. Draw the structures of the alkenes and rank them according to the amount that would be formed.

Textbook Question

a. Draw the structures of the products obtained from the reaction of each enantiomer of cis-1-chloro-2-isopropylcyclopentane with sodium methoxide in methanol.

b. Are all the products optically active?

Textbook Question

What are the products of the following reactions?

Textbook Question

What are the products of the following reactions?

Textbook Question

For each of the following reactions, draw the major elimination product; if the product can exist as stereoisomers, indicate which stereoisomer is obtained in greater yield.

d. trans-1-chloro-3-methylcyclohexane + high concentration of CH₃O⁻

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Draw the major elimination product that would be obtained from each of the following reactants with a strong base and with a weak base: a.

Key Concepts

Elimination Reactions

Strong vs. Weak Bases

Zaitsev's Rule

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Draw the major elimination product that would be obtained from each of the following reactants with a strong base and with a weak base:
a.