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Homework Help: Quick (and maybe dumb) question on chirality!

  1. Aug 17, 2009 #1
    1. The problem statement, all variables and given/known data

    How are my hands not constitutional isomers?

    3. The attempt at a solution

    I read this in a book today (Organic Chemistry for Dummies - good book actually), and I was covering chirality. Now, I am a bit shaky on it and need to go over it, but I got stuck on this for a while. The author stated that your hands are stereoisomers rather than consitiutional isomers.

    Here is my thought process...

    A constitutional isomer has the same molecular formula but some of the atoms are not in the same location. A stereoisomer is a molecule with the same molecular formula but a different 3D orientation.

    Now, for my point. My hands have the same molecular formula (4 fingers and one thumb). The thumb and pinky are not structurally in the same place from hand to hand. Isn't that what a constitutional isomer is? I mean, my hand still has the same molecular formula but just a different structure. It's like comparing butane to methylpropane, different structure but still an isomer.

    So what am I missing?
  2. jcsd
  3. Aug 17, 2009 #2


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    Staff: Mentor

    Mirror image.

    Actually, if you will list your fingers starting from thumbs, you will find out that both hands are identical - even if obviously they are not.

  4. Aug 17, 2009 #3


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    Science Advisor
    Homework Helper
    Gold Member

    Switch your thumb and your middle finger. Compare this constitutional isomer with the other hand. Not mirror images yet they have the same formula (4 fingers, 1 thumb).

    Compare your unaltered hands. Mirror images but not constitutional isomers. Middle finger in middle.... thumb off by itself, etc. These are stereoisomers.
  5. Aug 19, 2009 #4
    Thanks guys, I got it!
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