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

1. A Review of General Chemistry

Resonance Structures

Organic Chemistry

1. A Review of General Chemistry

Resonance Structures

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5:15 minutes

Problem 24b

Textbook Question

Benzyl bromide is a primary halide. It undergoes S_N1 substitution about as fast as most tertiary halides. Use resonance structures to explain this enhanced reactivity.

Verified step by step guidance

Begin by identifying the structure of benzyl bromide. Benzyl bromide consists of a benzene ring attached to a CH2 group, which is further bonded to a bromine atom.

Understand the concept of resonance. Resonance involves the delocalization of electrons across adjacent atoms, which can stabilize certain intermediates in a reaction.

When benzyl bromide undergoes SN1 substitution, the first step is the formation of a carbocation intermediate after the bromine leaves. This carbocation is formed at the benzylic position (the CH2 group attached to the benzene ring).

Examine the resonance stabilization of the benzylic carbocation. The positive charge on the carbocation can be delocalized into the benzene ring, creating multiple resonance structures. This delocalization stabilizes the carbocation, making the SN1 reaction more favorable.

Compare the stability of the benzylic carbocation to other carbocations. The resonance stabilization in benzyl bromide allows the carbocation to be as stable as those formed from tertiary halides, which typically have more stable carbocations due to hyperconjugation and inductive effects.

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Key Concepts

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

SN1 Reaction Mechanism

The SN1 reaction mechanism involves a two-step process where the leaving group departs first, forming a carbocation intermediate, followed by the nucleophile attacking the carbocation. This mechanism is typically favored by tertiary halides due to the stability of the carbocation formed, which is stabilized by hyperconjugation and inductive effects.

Carbocation Stability

Carbocation stability is crucial in SN1 reactions, as the rate-determining step involves the formation of a carbocation. Tertiary carbocations are generally more stable than primary ones due to greater hyperconjugation and inductive effects. However, benzyl carbocations are exceptionally stable due to resonance stabilization, which allows the positive charge to be delocalized over the aromatic ring.

Resonance Structures

Resonance structures are different Lewis structures for a molecule that depict the delocalization of electrons within the molecule. In benzyl bromide, the carbocation formed after the bromide leaves can be stabilized by resonance, as the positive charge is delocalized over the benzene ring. This delocalization enhances the stability of the carbocation, making the SN1 reaction more favorable despite benzyl bromide being a primary halide.

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Master The rules you need for resonance: with a bite sized video explanation from Johnny

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Benzyl bromide is a primary halide. It undergoes SN1 substitution about as fast as most tertiary halides. Use resonance structures to explain this enhanced reactivity.

Key Concepts

SN1 Reaction Mechanism

Carbocation Stability

Resonance Structures

Watch next

Benzyl bromide is a primary halide. It undergoes S_N1 substitution about as fast as most tertiary halides. Use resonance structures to explain this enhanced reactivity.