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

11. Radical Reactions

Allylic Bromination

Organic Chemistry

11. Radical Reactions

Allylic Bromination

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5:16 minutes

Problem 19a

Textbook Question

How many allylic substituted bromoalkenes are formed from the reactions in Problems 18 if stereoisomers are included?

Verified step by step guidance

Step 1: Analyze the reaction conditions. The reaction involves NBS (N-bromosuccinimide) in the presence of heat (Δ) and peroxide. This is a typical setup for allylic bromination, where bromine is introduced at the allylic position of an alkene.

Step 2: Identify the allylic positions in the given molecule. The molecule is cyclopentene, which has two allylic positions (the carbons adjacent to the double bond). These positions are equivalent due to the symmetry of the molecule.

Step 3: Consider the stereochemistry of the bromination. Bromination at the allylic position can lead to the formation of stereoisomers because the bromine atom can be added to either side of the planar allylic radical intermediate.

Step 4: Determine the possible products. Since the allylic positions are equivalent, bromination at either position will yield the same set of products. However, the stereoisomers arise due to the different spatial arrangements of the bromine atom relative to the double bond.

Step 5: Count the number of stereoisomers. For each allylic position, two stereoisomers (E and Z configurations) can be formed due to the double bond geometry. Since the allylic positions are equivalent, the total number of allylic substituted bromoalkenes formed, including stereoisomers, is the sum of these possibilities.

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Key Concepts

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

Allylic Bromination

Allylic bromination is a reaction where bromine is added to the allylic position of an alkene, typically using N-bromosuccinimide (NBS) in the presence of a radical initiator like peroxide. This reaction proceeds via a radical mechanism, where the allylic hydrogen is abstracted, forming a resonance-stabilized radical that can then react with bromine to form bromoalkenes.

Stereoisomerism

Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity but differ in the spatial arrangement of atoms. In the context of allylic bromination, the formation of stereoisomers occurs due to the presence of chiral centers or double bonds, leading to different geometric configurations (cis/trans or E/Z) in the resulting bromoalkenes.

Radical Mechanism

A radical mechanism involves the formation and reaction of free radicals, which are highly reactive species with unpaired electrons. In allylic bromination, the initiation step generates radicals that facilitate the bromination process. Understanding this mechanism is crucial for predicting the products and their stereochemistry, as radicals can lead to multiple pathways and product distributions.

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