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

19. Reactions of Aromatics: EAS and Beyond

Side-Chain Halogenation

Organic Chemistry

19. Reactions of Aromatics: EAS and Beyond

Side-Chain Halogenation

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14:10 minutes

Problem 55

Textbook Question

The solvent tetrahydrofuran (THF) is often sold with a small amount of BHT added. Provide a mechanism that explains why this might be so.

Verified step by step guidance

Tetrahydrofuran (THF) is a cyclic ether that is prone to oxidation when exposed to air, forming peroxides. These peroxides can be hazardous as they are potentially explosive.

Butylated hydroxytoluene (BHT) is a common antioxidant added to THF to prevent the formation of peroxides. BHT acts by donating a hydrogen atom to free radicals, thus terminating the radical chain reaction that leads to peroxide formation.

The mechanism begins with the initiation step where THF is exposed to oxygen, forming a THF radical and a superoxide radical.

In the propagation step, the THF radical reacts with oxygen to form a peroxide radical. This peroxide radical can further react with THF to form more radicals, continuing the chain reaction.

BHT intervenes in the chain reaction by donating a hydrogen atom to the peroxide radical, converting it into a non-radical species and thus stopping the propagation of the radical chain reaction.

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Key Concepts

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

Tetrahydrofuran (THF)

Tetrahydrofuran (THF) is a cyclic ether commonly used as a solvent in organic chemistry due to its ability to dissolve a wide range of polar and nonpolar compounds. Its structure features a five-membered ring with four carbon atoms and one oxygen atom, which contributes to its unique properties, including low viscosity and high dielectric constant. Understanding THF's reactivity and stability is crucial for grasping why additives like BHT are used.

BHT (Butylated Hydroxytoluene)

BHT, or Butylated Hydroxytoluene, is a synthetic antioxidant commonly added to various products to prevent oxidation. In the context of THF, BHT helps to inhibit the degradation of the solvent by scavenging free radicals that can form during storage or use. This preservation is essential for maintaining the solvent's effectiveness and preventing unwanted side reactions in chemical processes.

Free Radical Mechanism

The free radical mechanism involves the formation and reaction of free radicals, which are highly reactive species with unpaired electrons. In the presence of heat or light, THF can undergo autoxidation, leading to the generation of free radicals that can further react with the solvent, causing degradation. Understanding this mechanism is vital for explaining why BHT is added to THF, as it acts to stabilize the solvent by neutralizing these reactive intermediates.

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Predict the major products of the following reactions.

(f) p-methylanisole + Br₂ , light

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Predict the product of the following benzylic bromination reactions.

(b)

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Show how you would convert (in one or two steps) 1-phenylpropane to the three products shown below. In each case, explain what unwanted reactions might produce undesirable impurities in the product.

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A halogenation intended to make compound A formed B instead.

(b) Suggest a mechanism that rationalizes the formation of B.

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A halogenation intended to make compound A formed B instead.

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In the second propagation step in the bromination of toluene, Br₂ is only attacked by a radical on the substituent carbon. Why?

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For each compound, predict the major product of free-radical bromination. Remember that bromination is highly selective, and only the most stable radical will be formed.

(e)

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