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

16. Conjugated Systems

Conjugated Hydrohalogenation (1,2 vs 1,4 addition)

Organic Chemistry

16. Conjugated Systems

Conjugated Hydrohalogenation (1,2 vs 1,4 addition)

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4:35 minutes

Problem 35

Textbook Question

a. When HBr adds to a conjugated diene, what is the rate-determining step?
b. When HBr adds to a conjugated diene, what is the product-determining step?

Verified step by step guidance

The first step is to understand the mechanism of HBr addition to a conjugated diene. A conjugated diene contains alternating double and single bonds, which allow for delocalization of electrons. The reaction proceeds via an electrophilic addition mechanism.

In the rate-determining step, the π-electrons of one of the double bonds in the conjugated diene attack the electrophilic hydrogen (H⁺) from HBr. This results in the formation of a carbocation intermediate. The formation of this carbocation is the slowest step because it involves breaking the π-bond and creating a high-energy intermediate.

The next step is the product-determining step. Once the carbocation intermediate is formed, the bromide ion (Br⁻) attacks the positively charged carbon in the carbocation. The position of the bromide ion's attack depends on the stability of the carbocation intermediate, which can lead to either the 1,2-addition product or the 1,4-addition product.

To determine the major product, consider the stability of the carbocation intermediate and the reaction conditions. Under kinetic control (low temperature), the 1,2-addition product is favored because it forms faster. Under thermodynamic control (higher temperature), the 1,4-addition product is favored because it is more stable.

Finally, summarize the key points: The rate-determining step is the formation of the carbocation intermediate, and the product-determining step is the attack of the bromide ion on the carbocation, which determines whether the 1,2- or 1,4-addition product is formed.

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Key Concepts

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

Conjugated Dienes

Conjugated dienes are hydrocarbons that contain two double bonds separated by a single bond. This arrangement allows for resonance stabilization, which can influence the reactivity and stability of the molecule. Understanding the structure and behavior of conjugated dienes is crucial for predicting the outcomes of reactions, such as the addition of HBr.

Electrophilic Addition Mechanism

The electrophilic addition mechanism involves the reaction of an electrophile, like HBr, with a nucleophilic site in the diene. The first step typically involves the formation of a carbocation intermediate, which can lead to different products depending on the stability of the carbocation formed. Recognizing the steps in this mechanism is essential for determining both the rate-determining and product-determining steps in the reaction.

Carbocation Stability

Carbocation stability is a key factor in determining the outcome of reactions involving electrophilic addition. More stable carbocations, such as tertiary carbocations, are favored in reactions because they can better accommodate the positive charge. The stability of the carbocation formed during the reaction with HBr will influence both the rate of the reaction and the final product, making it a critical concept in understanding the overall process.

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