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NMR8. Chemical Shift in 1H NMR

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  • The trends here are exactly the same as in carbon spectra. Wherever the carbon goes, it takes the proton with it. By analogy with carbon spectra,

    • hydrogens on sp3 carbons usually show up in the upfield half of the spectrum, about 0 to 5 ppm.
    • hydrogens on sp2 carbons usually show up in the downfield half of the spectrum, about 5 to 10 ppm.
    • within these two halves of the spectrum, electronegative atoms attached to the same carbon as a proton will draw that proton downfield.

    NMR 1H9.gif

    Figure NMR11.1H NMR spectrum of hexane.

    Source: Simulated spectrum.

    NMR 1H10.gif

    Figure NMR12.1H NMR spectrum of 1-hexene.

    Source: Simulated spectrum.

    NMR 1H11.gif

    Figure NMR13.1H NMR spectrum of butanal.

    Source: Simulated spectrum.

    As before, there are also hydrogens on linear carbons, although they are much less common than tetrahedral or trigonal carbons.

    • hydrogens on sp carbons show up between 2 and 6 ppm.

    Remember, these are general rules that you should know. There will occasionally be exceptions; the proton in a carboxylic acid may be seen at 12 ppm, and the proton in chloroform shows up at 7 ppm although it is attached to a tetrahedral carbon. (World-record shifts occur for hydrogens attached to transition metals: "late" metals like ruthenium or rhodium can move hydrogen peaks all the way up to -20 ppm, but "early" metals like tantalum can move them down as far as 25 ppm.)

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