Is My Approach Correct for SN1 Reactions of Cyclic Ethers?

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Discussion Overview

The discussion revolves around the approach to understanding SN1 reactions of cyclic ethers, particularly focusing on the stability of carbocations and the role of leaving groups. Participants explore various aspects of the reaction mechanism, including the influence of molecular structure on reaction pathways.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant suggests that the presence of -Br as a leaving group in molecule (b) makes it more favorable for SN1 due to the acidic α hydrogen.
  • Another participant questions the initial analysis and emphasizes the importance of carbocation stability in determining the correct answer.
  • There is uncertainty regarding which carbocation is more stable, with one participant pondering whether molecule (a) is more stable due to charge separation or if (b) is more stable because of the polar C-O bond.
  • A question is raised about the stability of tertiary carbocations compared to primary ones, leading to a discussion on hyperconjugation.
  • Participants discuss hyperconjugation, with one explaining that it involves the interaction of σ electrons in adjacent orbitals, contributing to carbocation stability.
  • One participant expresses frustration with exam performance despite understanding concepts, seeking advice on managing exam pressure and mistakes.
  • Another participant offers general advice on practice and understanding concepts to reduce mistakes, but does not provide specific strategies.

Areas of Agreement / Disagreement

Participants express differing views on the stability of carbocations and the factors influencing SN1 reactions. There is no consensus on which molecular structure is definitively more stable or the best approach to the problem.

Contextual Notes

Participants acknowledge the complexity of carbocation stability and the influence of molecular structure on reaction pathways, but do not resolve these uncertainties.

Who May Find This Useful

Students studying organic chemistry, particularly those interested in reaction mechanisms and carbocation stability, may find this discussion relevant.

baldbrain
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The Attempt at a Solution


Firstly, since -Br is the better leaving group among the three, it's either (a) or (b). Further, since -Br is present at α position in (b), which also has an acidic α hydrogen to the same carbon, it would react better with a weak nucleophile (favouring SN1) than in (a). So, the answer's (b). But is my line of action correct?
 

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baldbrain said:
But is my line of action correct?
Not quite. If I had to guess, this question is really asking about carbocation stability. Your leaving group analysis is fine. So out of a and b, which carbocation is more stable?
 
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TeethWhitener said:
Not quite. If I had to guess, this question is really asking about carbocation stability. Your leaving group analysis is fine. So out of a and b, which carbocation is more stable?
Well, I can't really decide.
Is molecule (a) more stable because of separation of charges, or, is (b) more stable due to the highly polar C-O bond?
 
Why is a tertiary carbocation more stable than a primary one? (ignoring steric considerations)
 
Hyperconjugation
 
baldbrain said:
Hyperconjugation
Which is?
 
TeethWhitener said:
Which is?
Interaction of σ electrons in an adjacent empty π orbital.
 
baldbrain said:
Interaction of σ electrons in an adjacent empty π orbital.
Oh, so you mean the σ electrrons of the oxygen would interact with the π orbital of the carbocation, hence leading to more stability?
 
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baldbrain said:
Oh, so you mean the σ electrrons of the oxygen would interact with the π orbital of the carbocation?
Yes.
 
  • #10
TeethWhitener said:
Yes.
Ok. Thanks
 
  • #11
@TeethWhitener you didn't reply to my last question on 'How can any of these give the same SN1 & SN2 product'. I'd asked your advice on something
 
  • #12
What question?
 
  • #13
All my concepts are quite clear, but I still **** up during exams (probably due to haste). I also solve a lot of problems, and I can get them quicker when there's no time limit. That ticking clock makes me feel like a guillotine will behead me any moment.
Sometimes, even the opposite happens. I get the good problems, and **** up the easy ones. Can you give me some advice regarding this?
 
  • #14
I don't know if I’m the best one to give advice. Practice is the most important thing. People make mistakes occasionally. If you really understand a concept, then the number of mistakes will drop over time and become a kind of random noise. If you make an undue number of mistakes with particular concepts, it means you don’t quite understand it and you should seek outside help.
 
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  • #15
TeethWhitener said:
I don't know if I’m the best one to give advice. Practice is the most important thing. People make mistakes occasionally. If you really understand a concept, then the number of mistakes will drop over time and become a kind of random noise. If you make an undue number of mistakes with particular concepts, it means you don’t quite understand it and you should seek outside help.
All Right. Thank you again
 

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