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Mistake in TPR Organic? Pg 732

Discussion in 'MCAT Study Question Q&A' started by 0938h4gt983, Jun 20, 2008.

  1. 0938h4gt983

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    It says that a downfield shift causes the peak in the NMR to move to the left which corresponds with an increasing number.
    Then it says:
    Greater s-character -> more deshielding -> downfield shift -> left -> higher ppm
    But in the example:
    Propene (sp2)so character = 33%
    Propyne (sp)so character = 50%
    Which would mean:
    Propyne has greater s character -> more deshielding -> downward shift -> and a higher ppm

    BUT: propyne is 2 and propene is 6

    Do they mean more p character?
     
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  3. ThePandaFactor

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    No propyne has greater s character in it's bonds since they are sp instead of sp2.
     
  4. 0938h4gt983

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    Exactly, and if it has more s character it should have a higher ppm but it has a lower ppm
     
  5. ThePandaFactor

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    Oh ok I see what you are asking now. That rule is supposed to be just in general. The hydrogen at the end of the triple bond, though, experiences an induced magnetic field because of electron circulation, and thus counteracts the normal downward shift that you'd expect. Kind of like with benzene, there is a similar effect.
     

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