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Mass spectrum of pentan-3-one

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    In the above example, the molecular ion has fragmented into the cation [CH3CH2CO]+ (because the Mr of this is 57)..

    Would it be correct if you wrote [CH3CH2CO]+ as [C3H5O]+?

    Also could the molecular ion fragment into the below (instead of the above):

    [C4H9]+; since the Mr of this is also 57..

    Thanks
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    (Original post by sabre2th1)
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    Yes, you can write it like that, but the structural formula is better as it's more detailed.

    No it couldn't, as [CH3CH2CH2CH2]+ cannot be formed from CH3CH2COCH2CH3 (in terms of fragmentation), as in pentan-3-one, the oxygen is on the 3rd carbon, but there's no oxygen in [CH3CH2CH2CH2]+.
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    (Original post by thegodofgod)
    Yes, you can write it like that, but the structural formula is better as it's more detailed.

    No it couldn't, as [CH3CH2CH2CH2]+ cannot be formed from CH3CH2COCH2CH3 (in terms of fragmentation), as in pentan-3-one, the oxygen is on the 3rd carbon, but there's no oxygen in [CH3CH2CH2CH2]+.
    So each element (from the molecular ion) has to be present in the cation? And the number of atoms of each element present doesn't matter (as long as there is at least 1 atom of each, and overall it adds up to the peak's M/Z value)?
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    (Original post by sabre2th1)
    So each element (from the molecular ion) has to be present in the cation? And the number of atoms of each element present doesn't matter (as long as there is at least 1 atom of each, and overall it adds up to the peak's M/Z value)?
    No, sorry, what I wanted to express was that if you split [CH3CH2COCH2CH3]+ in any way, there is no way you can get [CH3CH2CH2CH2]+.

    What you've written above isn't correct :no:
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    (Original post by thegodofgod)
    No, sorry, what I wanted to express was that if you split [CH3CH2COCH2CH3]+ in any way, there is no way you can get [CH3CH2CH2CH2]+.

    What you've written above isn't correct :no:
    Oh I see. So in an exam question, if you were asked to write down the structural formula for a cation, how would you know if its right?

    Cheers
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    (Original post by sabre2th1)
    Oh I see. So in an exam question, if you were asked to write down the structural formula for a cation, how would you know if its right?

    Cheers
    You can normally work the structural formula out
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    (Original post by thegodofgod)
    You can normally work the structural formula out
    Oh okay, thank you

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