SN1 Carbocation Rearrangements - Ring Expansion Problems | Summary and Q&A

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March 20, 2023
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SN1 Carbocation Rearrangements - Ring Expansion Problems

TL;DR

Ring expansion reactions occur in alkyl halides, where a smaller ring can expand to form a more stable larger ring.

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Questions & Answers

Q: What determines the type of mechanism in ring expansion reactions?

The type of mechanism in ring expansion reactions is determined by the nature of the alkyl halide and the solvent. Secondary alkyl halides and protic solvents favor SN1 reactions, while tertiary alkyl halides and protic solvents favor S1 reactions.

Q: Why does a five carbon ring expand to a six carbon ring in ring expansion reactions?

Five carbon rings can expand to six carbon rings in ring expansion reactions because the formation of a six carbon ring is more stable. Six carbon rings are highly stable structures, which is why they do not undergo rearrangements.

Q: What happens when a four carbon ring undergoes ring expansion?

When a four carbon ring undergoes ring expansion, it can expand to a five carbon ring. The positive charge is placed on the carbon that has lost the bond to accommodate the expansion.

Q: Can ring expansion reactions occur with other solvents besides water and methanol?

Yes, ring expansion reactions can occur with other solvents as long as they are able to act as nucleophiles or bases. The choice of solvent can affect the type and outcome of the ring expansion reaction.

Summary & Key Takeaways

  • Ring expansion reactions involve alkyl halides reacting with water or methanol to form a more stable, larger ring.

  • The type of mechanism depends on the nature of the alkyl halide and the solvent used. In the examples provided, the reactions favor SN1 and S1 mechanisms.

  • In these reactions, the alkyl halide forms a carbocation intermediate, which can rearrange or undergo shifts before further reactions with water or methanol occur.

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