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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5:05 minutes

Problem 96c,d

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

Verified step by step guidance

Step 1: Recall the mechanism of an E2 reaction. E2 reactions are bimolecular eliminations where a base removes a β-hydrogen, and the leaving group departs simultaneously, forming a double bond. The reaction is stereospecific, favoring the anti-periplanar geometry of the β-hydrogen and the leaving group.

Step 2: Analyze the structure of 3-bromo-2,3-dimethylpentane. Identify the β-hydrogens available for elimination. Look for hydrogens on carbons adjacent to the carbon bonded to the bromine atom. Consider the anti-periplanar geometry to determine which β-hydrogen can be eliminated.

Step 3: Determine the stereoisomer formed in the elimination of 3-bromo-2,3-dimethylpentane. The anti-periplanar geometry dictates that the elimination will occur in a specific direction, forming the most stable alkene. Stability is influenced by factors such as substitution (more substituted alkenes are more stable) and steric hindrance.

Step 4: Analyze the structure of 3-bromo-3,4-dimethylhexane. Similar to the previous case, identify the β-hydrogens adjacent to the carbon bonded to the bromine atom. Again, focus on the anti-periplanar geometry to determine which β-hydrogen can be eliminated.

Step 5: Determine the stereoisomer formed in the elimination of 3-bromo-3,4-dimethylhexane. Consider the anti-periplanar geometry and the stability of the resulting alkene. The most substituted alkene will generally be favored, and steric hindrance should also be taken into account.

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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 occurs in a single step, leading to the formation of alkenes. The stereochemistry of the substrate plays a crucial role, as the reaction favors anti-periplanar geometry for optimal overlap of orbitals.

Stereochemistry and Stereoisomers

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. Stereoisomers are compounds with the same molecular formula and connectivity but different spatial orientations. In E2 reactions, the stereochemistry of the alkyl halide influences which stereoisomer is formed preferentially, often favoring the more stable trans or E isomer due to steric factors.

Zaitsev's Rule

Zaitsev's Rule states that in elimination reactions, the more substituted alkene (the one with more alkyl groups attached to the double bond) is typically the major product. This is because more substituted alkenes are generally more stable due to hyperconjugation and the inductive effect. Understanding this rule helps predict which stereoisomer will be formed in greater yield during E2 reactions involving alkyl halides.

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