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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3:45 minutes

Problem 96d

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

Verified step by step guidance

Identify the substrate: The given compound is 3-bromo-3,4-dimethylhexane, which is a tertiary alkyl halide. Tertiary alkyl halides are highly favorable for E2 elimination reactions due to steric hindrance that disfavors substitution reactions.

Recall the E2 mechanism: E2 elimination is a one-step concerted reaction where a base abstracts a β-hydrogen (hydrogen on a carbon adjacent to the carbon bearing the leaving group), and the leaving group (in this case, bromine) departs simultaneously, forming a double bond.

Determine the β-hydrogens: In 3-bromo-3,4-dimethylhexane, the β-carbons are the carbons adjacent to the carbon bonded to the bromine (C-3). These are C-2 and C-4. Examine the hydrogens on these β-carbons to identify possible elimination sites.

Apply anti-periplanar geometry: For the E2 reaction to proceed, the β-hydrogen and the leaving group (bromine) must be in an anti-periplanar (coplanar but opposite) arrangement. Analyze the Newman projection or the 3D structure of the molecule to determine which β-hydrogen satisfies this geometric requirement.

Predict the major product: The major product of the E2 reaction will be the most stable alkene, which is typically the more substituted alkene (Zaitsev's rule). Compare the possible alkenes formed by elimination at C-2 and C-4, and identify the stereoisomer with the greatest yield based on stability and anti-periplanar geometry.

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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 concerted process where a base abstracts a proton while a leaving group departs, resulting in the formation of a double bond. This mechanism typically requires a strong base and is stereospecific, favoring the formation of the more stable alkene. Understanding the stereochemistry involved is crucial for predicting the major product.

Stereochemistry and Alkene Stability

Stereochemistry refers to the spatial arrangement of atoms in molecules, which significantly influences the stability of alkenes. In E2 reactions, the formation of trans alkenes is generally favored over cis due to reduced steric strain. Recognizing the stereochemical outcomes helps in determining which isomer will be produced in greater yield.

Substituent Effects on Elimination Reactions

The presence and position of substituents on the alkyl halide can greatly affect the outcome of E2 reactions. Bulky groups near the leaving group can hinder the approach of the base, while more substituted alkenes are typically more stable due to hyperconjugation and inductive effects. Analyzing the structure of 3-bromo-3,4-dimethylhexane is essential to predict the major product.

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