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

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6:31 minutes

Problem 36a(1)

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.

Verified step by step guidance

Step 1: Begin by identifying the benzyl cation structure. The benzyl cation consists of a positively charged carbon atom directly attached to a benzene ring. This positive charge can be delocalized due to the conjugation with the π-electrons of the benzene ring.

Step 2: Draw the first resonance structure. The positive charge on the benzylic carbon can be delocalized into the benzene ring by shifting one of the π-electron pairs from the double bond adjacent to the benzylic carbon. This creates a double bond between the benzylic carbon and the benzene ring, while the positive charge moves to the ortho position of the benzene ring.

Step 3: Draw the second resonance structure. From the first resonance structure, shift another π-electron pair from the adjacent double bond in the benzene ring. This moves the positive charge to the para position of the benzene ring, while maintaining conjugation.

Step 4: Draw the third resonance structure. From the second resonance structure, shift another π-electron pair from the adjacent double bond in the benzene ring. This moves the positive charge to the other ortho position of the benzene ring.

Step 5: Summarize the resonance stabilization. The benzyl cation is stabilized by resonance because the positive charge is delocalized over four carbon atoms (the benzylic carbon and three carbons in the benzene ring). This delocalization reduces the energy of the cation, making it more stable than a simple alkyl cation.

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Key Concepts

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

Resonance

Resonance is a concept in organic chemistry that describes the delocalization of electrons in molecules where the bonding cannot be expressed by a single Lewis structure. Instead, multiple structures, known as resonance forms, are used to represent the molecule's electron distribution. This delocalization stabilizes the molecule, as seen in the benzyl cation, where the positive charge can be spread over several atoms, enhancing stability.

Benzylic Position

The benzylic position refers to the carbon atom directly attached to a benzene ring, specifically the carbon adjacent to the aromatic system. This position is significant because it exhibits unique reactivity patterns due to the influence of the benzene ring, which can stabilize intermediates like cations, anions, and radicals through resonance, making benzylic intermediates more stable than their non-aromatic counterparts.

Stability of Intermediates

In organic chemistry, the stability of intermediates such as cations, anions, and radicals is crucial for understanding reaction mechanisms. Benzylic cations, anions, and radicals are more stable than simple alkyl intermediates due to resonance stabilization provided by the adjacent benzene ring. This increased stability affects the reactivity and pathways of chemical reactions involving these intermediates.

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Related Practice

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

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?

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?

Textbook Question

Which species in each pair is more stable?

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