Question

When I made my NMR spectrum, I forgot to print it in `"Hz"` as well; how do I get coupling constants in `"Hz"`?

Answer 1

You don't need to do much more if you already got the chemical shifts in `"ppm"`.

All you have to do to convert to `"Hz"` is to multiply by the `"MHz"` of your NMR.

As an example, you should notice that the spacing between the shorter and taller peaks near `"3.5 ppm"` is about equal to the spacing between the shorter and taller peaks near `"1.2 ppm"`.

That likely means those protons are "communicating" and they happen to be neighboring.

These differences are approximately `3.665 - 3.654 = "0.011 ppm"` and `1.184 - 1.171 = "0.013 ppm"`.

If you have a `"300 MHz"` spectrometer, then:

`Deltadelta ~~ "0.012 ppm"`

`=> color(blue)(J_"HH")`

`= "0.012 ppm" xx "300 MHz"`

`= 0.012` `cancel("M"^(-1))` `xx` `300 cancel("M")"Hz"`

`=` `color(blue)("3.6 Hz")`

So once you find your chemical shifts, just choose the ones you want to find the coupling constants for, convert to `"Hz"`, subtract them, and that's your coupling constant (`J` value).