Why Am I Struggling with This Nucleophilic Reaction Problem?

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SUMMARY

The discussion centers on the challenges faced in solving a nucleophilic substitution reaction problem, specifically involving SN1 and SN2 mechanisms. The participant attempted to perform substitutions on a bromine atom but struggled with the geometry and stability of the carbocation. Key conclusions include the understanding that the bridgehead bromine does not participate in reactions due to its non-planar structure, making SN1 the more likely mechanism for the reaction involving the disubstituted carbocation.

PREREQUISITES
  • Nucleophilic substitution mechanisms (SN1 and SN2)
  • Carbocation stability and order
  • Geometric considerations in organic chemistry
  • Understanding of reaction conditions and nucleophile behavior
NEXT STEPS
  • Study the factors affecting carbocation stability in organic reactions
  • Learn about the geometric requirements for SN1 and SN2 reactions
  • Research the implications of bridgehead positions in cyclic compounds
  • Explore examples of nucleophilic substitution reactions involving different nucleophiles
USEFUL FOR

Chemistry students, organic chemists, and anyone studying nucleophilic substitution reactions will benefit from this discussion.

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.
 
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Oh. Sorry. It was an Sn1 on the non-bridgehead!
 
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