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    Hey. I have the following structure:


    There are 4 protons in the ring structure, but I'm getting confused as to whether they'd be in the same environment, or two different environments.

    Also I'm not sure if they'd be doublets or quartets?

    Any help is appreciated!
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    (Original post by StaShe)
    Hey. I have the following structure:


    There are 4 protons in the ring structure, but I'm getting confused as to whether they'd be in the same environment, or two different environments.

    Also I'm not sure if they'd be doublets or quartets?

    Any help is appreciated!
    Two different environments (the 2 closest to the Cl and the 2 closest to the alkyl chain). I would expect the peaks to be doublets (or dd with a tiny ^5 \text{J} coupling constant from the proton para), as there is no coupling between protons in the same environment bu there will be coupling between neighbouring protons.
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    Could you please explain this part?
    (Original post by alow)
    or dd with a tiny ^5 \text{J} coupling constant from the proton para), as there is no coupling between protons in the same environment bu there will be coupling between neighbouring protons.
    This is what I was referring to as a quartet but I haven't really done much on J-coupling so I'm not sure 100% how it works and what it'd look like in an NMR spectra?
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    (Original post by StaShe)
    Could you please explain this part?


    This is what I was referring to as a quartet but I haven't really done much on J-coupling so I'm not sure 100% how it works and what it'd look like in an NMR spectra?
    You can get coupling across the aromatic system, but the farther you get from the proton you're measuring, the closer together the split peaks will be. In these cases you usually get something that looks like a doublet but the very peak of the doublet is split in two.

    You only ever get a quartet when a proton couples to three protons each in unique environments.
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    (Original post by alow)
    You can get coupling across the aromatic system, but the farther you get from the proton you're measuring, the closer together the split peaks will be. In these cases you usually get something that looks like a doublet but the very peak of the doublet is split in two.

    You only ever get a quartet when a proton couples to three protons each in unique environments.
    True enough, but if you consider 5 bond coupling you'd also have to consider 4 bond coupling to chemically but not magnetically equivalent environments - smaller number of bonds + zig-zag relationship means I'm pretty sure 4J > 5J

    Basically, at A level the 'right' answer is two doublets from two environments, no need to worry about any longer range coupling!
 
 
 
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