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Isomery question

  1. May 22, 2013 #1
    The compound below is cis or trans?

    Fluoromethylpentene.png

    I learned that when the same ligants are at the same side of the bond, the isomerer is -cis, and when they are across, it is -trans. So I would say it is a cis compound

    Wikipedia, though, sai it is trans. They consider the backbone chain ligants. If the backbonechain ligants are at the same side it's cis, otherside, trans.

    So everything I learned was fake? I've seen nowhere else to treat cis/trans isomerer considering the backbone chain. What's the real answer?

    Thanks
    John
     
  2. jcsd
  3. May 22, 2013 #2

    Borek

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    Staff: Mentor

    cis-trans works for simple molecules, when it is obvious with substituents are the important ones - say but-2-ene - two methyls and two hydrogens, so it is obvious that we mean methyls to be cis or trans. In the case of a molecule like the one you posted it becomes more difficult, as it is not necessarily clear which two substituents are the important ones. Here it is better to use E/Z notation, as it is unambiguous.
     
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