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    Ok I'm still a little confused by this, how do you work out the highest peaks that occur in a compound in a mass spectrometer? Does the C-O bond break first and then C-C bonds around C-O bonds? Does a C-O bond break before a C=O? For example, CH3C(CH3)(2)C=OOCH3 the m/z = 57 and 85 are where the major peaks are found, but how come the C=O doesn't break to form a major peak and the C-O and C-C does? Does C-C break because the O pulls away the electrons away from the C atom and the bond weakens? :confused: thanks.. :rolleyes:
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    yes, O polarises the C-O bond. TBH with mass spec the ionisatio is kinda random, due to the random nature of bomabarding electrons - so you do get a nice mix of them all. They wont ask you to say why one particular fragment has occured, they'll just ask you to sugest an identity for it (so trial and error for me the :P)
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    (Original post by Asphyxiating)
    Ok I'm still a little confused by this, how do you work out the highest peaks that occur in a compound in a mass spectrometer? Does the C-O bond break first and then C-C bonds around C-O bonds? Does a C-O bond break before a C=O? For example, CH3C(CH3)(2)C=OOCH3 the m/z = 57 and 85 are where the major peaks are found, but how come the C=O doesn't break to form a major peak and the C-O and C-C does? Does C-C break because the O pulls away the electrons away from the C atom and the bond weakens? :confused: thanks.. :rolleyes:
    what exam board is it?
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    If you are doing AQA, I think you are supposed to know:

    • highest m/z value is parent ion (molecular ion), which give Mr of the compound
    • very common peaks eg 15=CH3, 29=CH2CH3
    • acyl (eg [COCH3]+) carbocations and tertiary carbocations (eg [(CH3)3C]+) are particularly stable, so they will show up as big (ie stable) peaks


    In the original question, I presume the compound is (CH3)3C-COOCH3...?

    m/z 57 = [(CH3)3C]+ *tertiary carbocation
    m/z 85 = [(CH3)3C-CO]+ *acyl carbocation

    Both are stable carbocations, thus they will form major peaks.

    Stability of the carbocation determines height of peaks... I don't think that bond strength play a particularly significant part, since the high energy electrons probably could break any bond in the compound. I think the stability decides which fragment become the carbocation (which is detected), and which fragment becomes the radical (which is not detected).

    selkie
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    (Original post by selkie222)
    If you are doing AQA, I think you are supposed to know:

    • highest m/z value is parent ion (molecular ion), which give Mr of the compound
    • very common peaks eg 15=CH3, 29=CH2CH3
    • acyl (eg [COCH3]+) carbocations and tertiary carbocations (eg [(CH3)3C]+) are particularly stable, so they will show up as big (ie stable) peaks


    In the original question, I presume the compound is (CH3)3C-COOCH3...?

    m/z 57 = [(CH3)3C]+ *tertiary carbocation
    m/z 85 = [(CH3)3C-CO]+ *acyl carbocation

    Both are stable carbocations, thus they will form major peaks.

    Stability of the carbocation determines height of peaks... I don't think that bond strength play a particularly significant part, since the high energy electrons probably could break any bond in the compound. I think the stability decides which fragment become the carbocation (which is detected), and which fragment becomes the radical (which is not detected).

    selkie
    Thank you, that really helps
 
 
 

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