Alkene Diastereomers Lab: Theory & Results

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Discussion Overview

The discussion revolves around a lab experiment involving alkene diastereomers, specifically maleic acid and fumaric acid. Participants express confusion regarding the purpose of the lab and the theoretical implications of the results, particularly in relation to the formation of diastereomers from a carbocation intermediate.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes a lab where maleic acid was reacted with a temporary carbocation, leading to the formation of either maleic acid or fumaric acid, and expresses confusion about the theoretical question regarding preferential formation of diastereomers.
  • Another participant questions the initial description of the experiment, suggesting a possible typo and requesting clarification on the full reaction.
  • A third participant offers an opinion that fumaric acid is more stable than maleic acid, citing steric hindrance in the cis conformation of maleic acid due to the positioning of functional groups.
  • A later reply reiterates the confusion about the lab's focus, correcting the initial claim that the lab was on alkene diastereomers and suggesting it was actually about geometric isomers, while also questioning the use of a temporary carbocation in the described reaction.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the details of the lab experiment or the theoretical implications. There are competing views regarding the stability of the diastereomers and the nature of the reaction conducted.

Contextual Notes

There are unresolved questions about the specific reaction conditions and mechanisms involved, as well as the definitions of terms like diastereomers and geometric isomers as applied in this context.

cmantzioros
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I did a lab on alkene diastereomers and I'm a bit confused as to what the purpose was. We reacted maleic acid with a temporary carbocation to see whether the product would be maleic acid or fumaric acid. These are alkene diastereomers of each other. My results suggested that the product was maleic acid.

I don't quite understand the theory... the pre-lab question said: "Will one of the alkene diastereomers be formed preferentially from the carbocation? If so, which one is favoured?" ... Can anyone tell me what this means?
 
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I don't quite understand the system you're asking about. I can only assume you made a typo whe you wrote "we reacted maleic acid with a temporary carbocation to see whether the product would be maleic acid or fumaric acid." Could you write out the full reaction? (no need to try including structures, that can be a hassle.)
 
Just eyeballing the structures, I would say fumaric acid is the more stable one; aside from generally being less stable, the cis conformation (maleic) is more sterically encumbered because of the two functional groups on the same side.
 
cmantzioros said:
I did a lab on alkene diastereomers and I'm a bit confused as to what the purpose was. We reacted maleic acid with a temporary carbocation to see whether the product would be maleic acid or fumaric acid. These are alkene diastereomers of each other. My results suggested that the product was maleic acid.

I don't quite understand the theory... the pre-lab question said: "Will one of the alkene diastereomers be formed preferentially from the carbocation? If so, which one is favoured?" ... Can anyone tell me what this means?

First, you did not do a lab on alkene diastereomers. You did a lab on geometric isomers (cis/trans). Could you please explain what you mean by "we reacted maleic acid with a temporary cation to see whether the product would be maleic acid or fumaric acid"? When I taught that lab we used an acid catalyst on maleic acid to study the isomerism. It went through a carbocation intermediate but it was not reacted with one.
 

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