19F NMR

19F NMR

According to quantum mechanics, any nucleus is magnetically active if it possess a nonzero angular moment, P, which gives rise to a nuclear magnetic moment, µ, capable of interacting with an external magnetic field (Eq. 1).

(1)                                 µ = γP

The magnetogyric ratio, γ, is the ratio of magnet moment to angular momentum. It relates the magnetic resonance (MR) frequency of a nuclide and the strength, or sensitivity of response of interaction of the nuclide when it is subjected to an external magnetic field. The 1H nucleus has the largest γ value (26.752 107 rad T-1 s-1) of stable isotopes on the NMR periodic table, making it the most sensitive to nuclear resonance excitation. The 19F nuclide comes next with a high magnetogyric ratio (25.18 107 rad T-1 s-1) at 94% of 1H, and has the advantage of 100% natural abundance. In combination, the result is a high relative sensitivity of 83% for fluorine.

With a dedicated Thermo Scientific™ picoSpin™ 45 19F NMR spectrometer, measuring19F NMR spectra in a bench-top instrument is as easy as acquiring proton spectra from the picoSpin™ 45 1H NMR spectrometer. A dedicated 19F spectrometer is tuned to the fluorine Larmor frequency (42.4 MHz) to yield the highest sensitivity for this nuclide. This application note presents 19F NMR spectra acquired from highly fluorinated small organic compounds, demonstrating the wealth of spectral information obtained from a bench-top picoSpin™ 45 19F NMR spectrometer.

Figure 1. Full 19F NMR (42.4 MHz) spectrum of hexaflourobenzene (neat); 25 scans

Figure 2. Full 19F NMR (42.4 MHz) spectrum of octafluorotoluene (neat); 36 scans

Figure 3. Full 19F NMR (42.4 MHz) spectrum of 2H,3H-decafuoropantane (neat)

Figure 4. Full 19F NMR (42.4 MHz) spectrum of hexafluoroisopropanol in trifluorotoluene (70:30 v/v)

Figure 5. Full 1H NMR (45 MHz) spectrum of hexafluoroisopropanol in trifluorotoluene (70:30 v/v)