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    I really dislike this topic because I never know how to answer te questions

    I approached it like this
    1) 5 carbon environments
    2) mr of 106
    Then I got stuck

    Can someone guide me through this question
    Thanks


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    (Original post by Lilly1234567890)
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    I really dislike this topic because I never know how to answer te questions

    I approached it like this
    1) 5 carbon environments
    2) mr of 106
    Then I got stuck

    Can someone guide me through this question
    Thanks


    Posted from TSR Mobile
    Use the mass spectrum to get the molecular ion and hence the relative mass = 106

    You know that its aromatic, so it must have at least 6 carbon atoms = 72 mass units. Hence there are 106 - 72 = 34 mass units left to find. There will be a few hydrogen atoms floating around so that leaves only 2 carbon atoms.
    Mass of carbon atoms = 8 x 12 = 96
    So there are 10 hydrogen atoms.

    There are only two possibilities:

    dimethylbenzene
    ethylbenzene

    The dimethylbenzene could be:
    1,2-dimethylbenzene
    1,3-dimethylbenzene
    1,4-dimethylbenzene

    That means in total there are four possible structures.

    Now we consider how many different carbon environments each structure would have.

    ethylbenzene = 6 different environments
    1,2-dimethylbenzene = 4 different environments
    1,3-dimethylbenzene = 5 different environments
    1,4-dimethylbenzene = 3 different environments

    so you look at the number of signals in the 13C NMR and count them!

    There are five.

    1,3-dimethylbenzene (otherwise known as meta-xylene)
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    (Original post by charco)
    Use the mass spectrum to get the molecular ion and hence the relative mass = 106

    You know that its aromatic, so it must have at least 6 carbon atoms = 72 mass units. Hence there are 106 - 72 = 34 mass units left to find. There will be a few hydrogen atoms floating around so that leaves only 2 carbon atoms.
    Mass of carbon atoms = 8 x 12 = 96
    So there are 10 hydrogen atoms.

    There are only two possibilities:

    dimethylbenzene
    ethylbenzene

    The dimethylbenzene could be:
    1,2-dimethylbenzene
    1,3-dimethylbenzene
    1,4-dimethylbenzene

    That means in total there are four possible structures.

    Now we consider how many different carbon environments each structure would have.

    ethylbenzene = 6 different environments
    1,2-dimethylbenzene = 4 different environments
    1,3-dimethylbenzene = 5 different environments
    1,4-dimethylbenzene = 3 different environments

    so you look at the number of signals in the 13C NMR and count them!

    There are five.

    1,3-dimethylbenzene (otherwise known as meta-xylene)
    Oh waw thanks !


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