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

Stability of Conjugated Intermediates

Organic Chemistry

16. Conjugated Systems

Stability of Conjugated Intermediates

Previous problemNext problem

4:33 minutes

Problem 29

Textbook Question

Which of the double bonds in zingiberene, the compound responsible for the aroma of ginger, is most reactive in an electrophilic addition reaction with HBr?

Verified step by step guidance

Identify the structure of zingiberene from the image. Zingiberene contains three double bonds labeled as 1, 2, and 3. These double bonds are located in different positions within the molecule, and their reactivity in electrophilic addition reactions depends on their electronic environment and steric factors.

Understand the mechanism of electrophilic addition of HBr. In this reaction, the π-electrons of the double bond attack the electrophilic hydrogen (H⁺) of HBr, forming a carbocation intermediate. The stability of this carbocation intermediate is a key factor in determining which double bond is most reactive.

Analyze the stability of the carbocation intermediates formed by each double bond. Double bond 1 forms a secondary carbocation, double bond 2 forms a tertiary carbocation, and double bond 3 forms a primary carbocation. Tertiary carbocations are the most stable due to hyperconjugation and inductive effects, followed by secondary and then primary carbocations.

Consider steric hindrance and accessibility. Double bond 2 is located in a less sterically hindered position compared to double bond 1 and double bond 3, making it more accessible for the electrophilic addition reaction.

Conclude that double bond 2 is the most reactive in an electrophilic addition reaction with HBr because it forms the most stable carbocation (tertiary) and is in a relatively accessible position within the molecule.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Electrophilic Addition Reactions

Electrophilic addition reactions involve the addition of an electrophile to a nucleophile, typically across a double bond. In alkenes, the π bond is broken, allowing the electrophile to bond with one carbon atom while a nucleophile can bond with the other. The reactivity of the double bond is influenced by factors such as sterics and electronic effects, which determine how readily the double bond can react with electrophiles like HBr.

Stability of Carbocation Intermediates

During electrophilic addition, a carbocation intermediate is often formed. The stability of this carbocation is crucial for determining the reactivity of the double bond. More stable carbocations, such as tertiary carbocations, are formed from more substituted double bonds, making those bonds more reactive in electrophilic addition reactions. Understanding the stability of these intermediates helps predict which double bond will react preferentially.

Regioselectivity in Electrophilic Addition

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the context of electrophilic addition to alkenes, the Markovnikov rule often applies, stating that the more substituted carbon will bond with the electrophile. This concept is essential for predicting the outcome of the reaction with HBr in zingiberene, as it helps identify which double bond will be more reactive based on the structure of the compound.

Watch next

Master Stability of Conjugated Intermediates with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

Draw the important resonance contributors for the following cations, anions, and radicals.

(b)

Textbook Question

Draw the important resonance contributors for the following cations, anions, and radicals.

(c)

Textbook Question

Draw the important resonance contributors for the following cations, anions, and radicals.

(d)

Textbook Question

Draw the important resonance contributors for the following cations, anions, and radicals.

(e)

(f)

Textbook Question

The benzene ring alters the reactivity of a neighboring group in the benzylic position much as a double bond alters the reactivity of groups in the allylic position.

Benzylic cations, anions, and radicals are all more stable than simple alkyl intermediates.

a. Use resonance forms to show the delocalization (over four carbon atoms) of the positive charge of the benzyl cation.

Textbook Question

The benzene ring alters the reactivity of a neighboring group in the benzylic position much as a double bond alters the reactivity of groups in the allylic position.

Benzylic cations, anions, and radicals are all more stable than simple alkyl intermediates.

a. Use resonance forms to show the delocalization (over four carbon atoms) of the unpaired electron of the benzyl radical.

Textbook Question

The benzene ring alters the reactivity of a neighboring group in the benzylic position much as a double bond alters the reactivity of groups in the allylic position.

Benzylic cations, anions, and radicals are all more stable than simple alkyl intermediates.

c. Which of the following reactions will have the faster rate and give the better yield? Use a drawing of the transition state to explain your answer.

Textbook Question

Which species in each pair is more stable?

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap