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Alkene diastereomers

  1. Mar 12, 2008 #1
    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?
     
  2. jcsd
  3. Mar 13, 2008 #2
    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.)
     
  4. Mar 13, 2008 #3
    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.
     
  5. Mar 14, 2008 #4

    chemisttree

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    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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