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    Hi, I need help understanding something..
    Electronegative compounds should have lower chemical shift values right? as less energy is required to resonate the molecule as its less shielded. So why on the chemical shift values the c-c bond is at the lower end and needs less energy compared to c-br, c-cl,c-o compounds? Hope this makes sense.

    Also the engery is required to resonate the carbon 13 molecule so does this mean all the compounds must have carbon13? Sorry these Q must sound stupid.
    Thanks.
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    For Hydrogen/Proton NMR, if a hydrogen is within three bonds of an more electronegative element (e.g Oxygen) then it will have a higher chemical shift value. (further left)
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    (Original post by gozatron)
    For Hydrogen/Proton NMR, if a hydrogen is within three bonds of an more electronegative element (e.g Oxygen) then it will have a higher chemical shift value. (further left)
    shouldnt it have a lower chemical shift value cause less magnetic field engergy is required to flip it?
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    ohhh my i'm so confused :/
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    (Original post by hey-hey-hey)
    ohhh my i'm so confused :/
    Pulling electron density away from a nucleus de-sheilds it. Essentially exposing it to a bigger magnetic field. A bigger magnetic field acting on the nucleus causes a bigger splitting between the two possible energy states. A bigger splitting between the two possible energy states means that a larger amount of energy is absorbed for reasonance...

    The important thing to remember is that the energy absorbed is at a single value, that unique amount of energy absorbed is unique to that particular nucleus, this is why NMR is so useful, it tells you what nucleus is present, and where it's present in the molecule.
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    (Original post by hey-hey-hey)
    shouldnt it have a lower chemical shift value cause less magnetic field engergy is required to flip it?
    The NMR shift scale goes from right to left, not left to right.

    Be careful. Yeah, chemists are stupid, I don't know why the scale is that way.
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    (Original post by Inkerman)
    The NMR shift scale goes from right to left, not left to right.

    Be careful. Yeah, chemists are stupid, I don't know why the scale is that way.

    thank you so much! I really appreciate it..so basically
    so the chemical shift values is the measure of magnetic field strength and molecules that are shielded have a lower chemical shift value cause the nucleus isn’t feeling the strength of the mag field...and molecules that are de-shielded have a higher value cause they're absorbing the energy more. Is this right?
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    (Original post by hey-hey-hey)
    thank you so much! I really appreciate it..so basically
    so the chemical shift values is the measure of magnetic field strength and molecules that are shielded have a lower chemical shift value cause the nucleus isn’t feeling the strength of the mag field...and molecules that are de-shielded have a higher value cause they're absorbing the energy more. Is this right?
    The chemical shift value is really just an amount in Hertz...an amount of energy.

    That amount of energy is really just the difference between two energy levels

    Amount of energy = energy level 1 - energy level 2


    Of course, the difference between those two energy levels (and therefore the amount of energy) depends on the magnetic field, how? Well, a bigger field increases the gap between the two levels...

    Or, you can remove electrons from the nucleus with electronegative elements, deshielding it, this means that the nucleus 'feels' a bigger magnetic field....it seems as if there is a larger magnetic field...you understand?
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    (Original post by Inkerman)
    The chemical shift value is really just an amount in Hertz...an amount of energy.

    That amount of energy is really just the difference between two energy levels

    Amount of energy = energy level 1 - energy level 2


    Of course, the difference between those two energy levels (and therefore the amount of energy) depends on the magnetic field, how? Well, a bigger field increases the gap between the two levels...

    Or, you can remove electrons from the nucleus with electronegative elements, deshielding it, this means that the nucleus 'feels' a bigger magnetic field....it seems as if there is a larger magnetic field...you understand?
    Yeahh i do, so if a molecule is sheilded it will show up at the far left of the spectra with a higher chemical shift value yeah?becuase of the reasons you mentioned right? thankyou!
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    (Original post by hey-hey-hey)
    Yeahh i do, so if a molecule is sheilded it will show up at the far left of the spectra with a higher chemical shift value yeah?becuase of the reasons you mentioned right? thankyou!
    ...

    The graph goes from right to left. Increasing energy as you go from right to left.

    If a molecule is shielded it will show up on the far right with a lower chemical shift value because it feels a smaller magnetic field...
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    (Original post by Inkerman)
    ...

    The graph goes from right to left. Increasing energy as you go from right to left.

    If a molecule is shielded it will show up on the far right with a lower chemical shift value because it feels a smaller magnetic field...
    oops yep I ment it the other way around...thank you I understand it now, really really appreciate your help!!
 
 
 
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