¹⁹F Experiments with Proton Decoupling

Measuring ¹⁹F spectra with proton decoupling, or ¹H spectra with fluorine decoupling differs from the conventional heteronuclear decoupling, because the spectrometers have only one high band amplifier, which has to be shared between the proton and fluorine pulses. This will be taken care off by setting homo=’y’. Other than that, the set-up procedure is similar to that of normal decoupling:

1. Collect a fluorine FID using the standard parameters and process the data.
2. Determine the spectral window you want to observe. Using the left and right mouse buttons, bracket the spectral range that you want to observe. Be aware, that peaks outside your cursors may fold in, meaning they may appear with strange phases at places in the spectrum, which do not correspond to their true shifts. Typing movesw will set the center frequency and sweep width to correspond to your choice.
3. jexp2 join an other experiment, for example 2, if not used and collect a standard proton experiment.
4. Find the peak, which you want to decouple with and set your cursor on it.
5. nl
6. movetof
7. tof? will give you the exact offset frequency, write it down.
8. jexp1 go back to your fluorine spectrum in experiment 1, if that was what you used.
9. dn=’H1’
10. dof= enter the offset you found as tof in the proton experiment
11. dm=’nny’ this allows proton decoupling during the acquisition
12. dmm=’c’ turns on "continuos" wave decoupling (see remark below)
13. homo=’y’ allows the use of the high band amplifier for both nuclei
14. Next you need to find the minimum decoupler power, that is sufficient for you to collapse the multiplet you wish to decouple. You do this by arraying dpwr (see PulseWidth / Delays on how to array). Rough values to test may be between 40 and 49. Do not go higher than 49 or you will ruin the probe.

Now you are ready to get your data, good luck.

Remark:

You may want to use different decoupling schemes (dmm= ‘w’, (WALTZ-16), ‘m’, (MLEV-16), or ‘g’, (GARP)). For these it is important to set dmf which corresponds the inverse of the decoupling pulselenghts. Because of the necessity to share the amplifier between both nuclei it is not possible for all sweepwidths, to use all dmf values. We recommend, that you array dmf and optimize the value for your goal. You may also want to do a proton homonuclear decoupled experiment, to see, which proton resonances are effected with your values of choice.  

The following table gives you an idea about possible decoupler settings for the standard sweepwidth (133333 Hz). Optimize the parameters for your system. 

decoupler scheme	dpwr	max dmf that gives decoupling
c	31	not used
w	48	1500
g	48	3000
m	48	4000