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    I have M = butanoic acid, N = ethyl ethanoate

    For M,

    I have m/e peaks at 56 and 60.

    For N,

    I have m/e peaks at 61.

    What species causes these peaks.

    I tried breaking these molecules up, but can't find a species corresponding to that m/e

    Thanks in advance
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    butanoic acid = (CH3)(CH2)(CH2)(CO2H) = 88

    knock off the acid hydrogen:
    (CH3)(CH2)(CH2)(CO2)

    knock off the starting ethyl group:
    (CH2)(CO2)

    knock 2 protons off the CH2
    (C)(CO2) = 56

    not sure about the other 2. my brain hurts
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    1.1% of natural carbon is the C13 isotope which can lead to M+1 readings in the mass spectrum of organic molecules.

    I don't know anything about which sites an organic molecule preferentially splits at but perhaps for butanoic acid, the 60 mark is from
    +H2c- c -OH with one of the carbons being C13
    ........||
    .........O

    And for ethyl ethanoate, the 61 mark might be from:

    +O - C -CH3 with both carbons being C13
    ......||
    ......O
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    (Original post by oceane)
    1.1% of natural carbon is the C13 isotope which can lead to M+1 readings in the mass spectrum of organic molecules.

    I don't know anything about which sites an organic molecule preferentially splits at but perhaps for butanoic acid, the 60 mark is from
    +H2c- c -OH with one of the carbons being C13
    ........||
    .........O

    And for ethyl ethanoate, the 61 mark might be from:

    +O - C -CH3 with both carbons being C13
    ......||
    ......O
    For the first one, the peak would be very small

    And for the second one, I doubt the mass specrometer would have a great enough resolution to register it, since only 0.01% of the molecules would contain 2 C13 atoms, and then these would have to be in the right position.

    Basically, these peaks would probably be too small to show up on the spectra.

    Nice thought though, it just happens that C13 doesnt occur in large enough amounts naturally
    • Thread Starter
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    Can some one please help me:

    I have M = butanoic acid, N = ethyl ethanoate

    For M,

    I have a m/e peak 60.

    For N,

    I have m/e peaks at 61.

    What species causes these peaks.

    I tried breaking these molecules up, but can't find a species corresponding to that m/e

    Thanks in advance
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    The only way of getting an m/z value of 60 for butanoic acid is to have the following fragment, as Oceane has already explained:

    +CH2COOH

    With one of the carbons being the isotope 13C
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    And the only way of getting 61 for ethyl ethanoate, is to have the following fragment, as Oceane has also explained:

    CH3COO+

    With both carbons being the isotope 13C. I know its highly unlikely, but it could happen.
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    Thing is this... the peaks for 60 and 61 are quite high...
 
 
 
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