Why Am I Struggling with This Nucleophilic Reaction Problem?

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Discussion Overview

The discussion revolves around a nucleophilic reaction problem involving substitution reactions (SN1 and SN2) and the stability of carbocations. Participants explore the feasibility of reactions at specific sites in a molecular structure, particularly focusing on the implications of geometry and the role of bromine atoms in the reaction process.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses difficulty in solving a nucleophilic reaction problem, specifically regarding substitution reactions at a bromine atom.
  • Another participant questions the order of carbocation stability, suggesting it may influence the reaction pathway.
  • Participants discuss the likelihood of SN1 versus SN2 mechanisms based on the geometry of the molecular structure.
  • There is a proposal that SN2 may be less likely due to geometric constraints preventing backside attack on the halogenated carbons.
  • Concerns are raised about the stability and planarity of the bridgehead bromine, with some participants suggesting it does not participate in reactions.
  • One participant concludes that the reaction would likely be SN1 due to geometric limitations, while another confirms this reasoning.
  • There is a moment of confusion regarding whether the reaction occurs at the bridgehead or non-bridgehead site, with participants expressing uncertainty about their conclusions.

Areas of Agreement / Disagreement

Participants express differing views on the likelihood of SN1 versus SN2 mechanisms and the role of the bridgehead bromine in the reaction. The discussion remains unresolved regarding the exact nature of the reaction and the implications of geometry on the reaction pathways.

Contextual Notes

Participants reference geometric constraints and carbocation stability without reaching a consensus on how these factors definitively affect the reaction outcome. There are also unresolved assumptions about the behavior of the bridgehead bromine in the reaction.

Natalie456
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I have attempted this problem several times, but I keep on getting an incorrect answer. I have tried mostly substitution reactions (SN1 and SN2) on the top bromine atom, and I know that a double bond cannot be formed at the bridgehead. Any help in the right direction is greatly appreciated. Thanks!

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What is the order of carbocation stability?
 
Also, given the geometry of the problem, is SN1 or SN2 more likely?
 
Would SN2 be more likely? I tried a substitution at the top bromine atom with the nucleophile -CN, but it was incorrect. I'm not sure where to go from there. For SN1, the carbocation at the top would be disubstituted. I'm assuming that the bromine at the bridgehead doesn't participate in any reactions.
 
Natalie456 said:
I'm assuming that the bromine at the bridgehead doesn't participate in any reactions.
Why not?
 
Natalie456 said:
Would SN2 be more likely?
Geometrically, does it look like a nucleophile will be able to attack the backside of either of the halogenated carbons?
 
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I guess, geometrically, it doesn't look like it will be able to attack either from the backside. So it would be an SN1, then? Also, I thought there could be no reaction at the bridgehead because it cannot be planar, or it is too unstable. Is this correct?
 
I got it! Thank you so much for helping me reason through it!
 
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Natalie456 said:
Also, I thought there could be no reaction at the bridgehead because it cannot be planar, or it is too unstable. Is this correct?
Yes, that sounds right. Ignore where I was going before with that.

Natalie456 said:
I guess, geometrically, it doesn't look like it will be able to attack either from the backside. So it would be an SN1, then?
This would be my guess.
 
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Natalie456 said:
I got it! Thank you so much for helping me reason through it!
Well, now I've thoroughly confused myself. Was it an Sn1 on the non-bridgehead? I need more caffeine.
 
  • #11
Oh. Sorry. It was an Sn1 on the non-bridgehead!
 
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