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

9. Alkenes and Alkynes

Zaitsev Rule

Organic Chemistry

9. Alkenes and Alkynes

Zaitsev Rule

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4:07 minutes

Problem 89e,f

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.
e. 3-bromo-3-methylpentane + high concentration of CH₃CH₂O⁻
f. 3-bromo-3-methylpentane + CH₃CH2OH

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Identify the type of elimination reaction (E1 or E2) for each scenario. For reaction (e), the presence of a strong base (CH3CH2O−) and high concentration suggests an E2 mechanism. For reaction (f), the use of a weaker base/nucleophile (CH3CH2OH) suggests an E1 mechanism.

For the E2 reaction (e), analyze the structure of 3-bromo-3-methylpentane. The β-hydrogens (hydrogens on carbons adjacent to the carbon bearing the leaving group) are located on the second and fourth carbons. Identify the β-hydrogens that are anti-periplanar to the leaving group (bromine).

In the E2 mechanism, the elimination occurs in a single concerted step. The base (CH3CH2O−) abstracts a β-hydrogen, the C-H bond breaks, and the C-Br bond breaks simultaneously, forming a double bond. Determine the major product by applying Zaitsev's rule, which states that the more substituted alkene is favored.

For the E1 reaction (f), the first step is the ionization of the C-Br bond to form a carbocation intermediate. Since 3-bromo-3-methylpentane forms a tertiary carbocation, it is highly stable. Next, a β-hydrogen is removed by the weak base (CH3CH2OH), leading to the formation of the alkene.

For both reactions, if the product can exist as stereoisomers (E/Z or cis/trans), determine the stereoisomer that is formed in greater yield. In E2 reactions, the anti-periplanar geometry often dictates the stereochemistry. In E1 reactions, the product distribution is governed by thermodynamic stability, favoring the more stable stereoisomer (usually the E isomer).

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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 small molecule from a larger one, typically resulting in the formation of a double bond. In organic chemistry, these reactions can follow either E1 or E2 mechanisms, depending on the conditions and the structure of the substrate. Understanding the mechanism is crucial for predicting the major product and its stereochemistry.

Stereochemistry

Stereochemistry refers to the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In elimination reactions, the stereochemistry of the product can lead to different stereoisomers, such as cis and trans forms. Recognizing which stereoisomer is favored in a reaction is essential for determining the major product.

Regioselectivity

Regioselectivity is the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In the context of elimination reactions, this concept helps predict which alkene product will be formed based on the stability of the resulting double bond. Factors such as sterics and electronic effects play a significant role in determining the regioselectivity of the reaction.

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For each of the following compounds, draw the product that forms in an E2 reaction and indicate its configuration:

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(a)

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When using sulfuric acid, but in the absence of other nucleophiles like water or bromide ion, less stable alkenes can be isomerized to their more stable isomer. Provide a mechanism for these acid-catalyzed isomerization reactions. [This is one illustration of the principle of microscopic reversibility.]

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Which alkyl halide in each pair is more reactive in an E2 reaction with hydroxide ion?

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What products will be obtained from the E2 reaction of the following alkyl halides?

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Draw the elimination products for each of the following E2 reactions; if the products can exist as stereoisomers, indicate which stereoisomers are obtained.

d. (2R,3R)-2-chloro-3-methylpentane + high concentration of CH₃O^-

Textbook Question

What is the major elimination product obtained from an E2 reaction of each of the following alkyl halides with hydroxide ion?

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