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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9:37 minutes

Problem 25c,d

Textbook Question

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

Verified step by step guidance

Step 1: Understand the E2 reaction mechanism. E2 reactions are bimolecular elimination reactions where a base removes a proton from a β-carbon, and a leaving group (such as Br) departs simultaneously, forming a double bond.

Step 2: Analyze the first pair of alkyl halides. The reactivity in E2 reactions depends on the ability of the β-hydrogen to be abstracted and the stability of the resulting alkene. The first structure is a secondary alkyl bromide, while the second structure is a primary alkyl bromide. Secondary alkyl halides are generally more reactive in E2 reactions due to the formation of a more stable alkene.

Step 3: Analyze the second pair of alkyl halides. Both structures contain a benzene ring, which can stabilize the resulting alkene through conjugation. The first structure has the bromine attached to a secondary carbon, while the second structure has the bromine attached to a primary carbon. The secondary alkyl bromide is more reactive in E2 reactions due to the stability of the alkene formed.

Step 4: Consider steric hindrance. In E2 reactions, steric hindrance around the β-hydrogen can affect the reaction rate. Secondary alkyl halides typically have less steric hindrance compared to tertiary alkyl halides, making them more reactive.

Step 5: Summarize the findings. For the first pair, the secondary alkyl bromide is more reactive. For the second pair, the secondary alkyl bromide attached to the benzene ring is more reactive due to the stabilization provided by conjugation with the aromatic ring.

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Key Concepts

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

E2 Reaction Mechanism

The E2 (bimolecular elimination) reaction is a type of elimination reaction where a base removes a proton from a β-carbon while a leaving group departs from the α-carbon simultaneously. This concerted mechanism results in the formation of a double bond. The strength of the base and the structure of the alkyl halide significantly influence the reaction rate and outcome.

Alkyl Halide Reactivity

The reactivity of alkyl halides in E2 reactions is influenced by steric hindrance and the nature of the leaving group. Generally, tertiary alkyl halides are more reactive than secondary, which are more reactive than primary halides due to steric factors that affect the accessibility of the β-hydrogen to the base. A better leaving group also enhances reactivity.

Role of Hydroxide Ion

Hydroxide ion (OH-) is a strong base commonly used in E2 reactions. Its ability to abstract a proton from the β-carbon is crucial for the elimination process. The strength of the base can affect the reaction pathway, and in the presence of a strong base like hydroxide, the E2 mechanism is favored over substitution reactions.

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Related Practice

Textbook Question

Predict the major product(s) of the following elimination reactions, paying close attention to the stereochemical outcome of the reactions.

(b)

Textbook Question

a. What is the major product obtained when each of the following compounds undergoes an E2 reaction with methoxide ion? Show the configuration of the product.

b. Does the product obtained depend on whether you start with the R or S enantiomer of the reactant?

Textbook Question

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

Textbook Question

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

Textbook Question

For each of the following alkyl halides, indicate the stereoisomer that would be obtained in greatest yield in an E2 reaction.

c. 3-bromo-2,3-dimethylpentane

d. 3-bromo-3,4-dimethylhexane

Textbook Question

For each of the following alkyl halides, indicate the stereoisomer that would be obtained in greatest yield in an E2 reaction.

d. 3-bromo-3,4-dimethylhexane

Textbook Question

What is the major product formed when the following compounds undergo an E1 reaction?

Textbook Question

Draw the major product obtained when an alkyl halide in [PROBLEM 9-83] undergoes an E1 reaction.

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

Key Concepts

E2 Reaction Mechanism

Alkyl Halide Reactivity

Role of Hydroxide Ion

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