F19 Detection

F19 is a sensitive nucleus to detect. On most probes it is detected through the same RF and preamp as for H1. Unlike H1, F19 has an extremely wide chemical shift range, spanning +/- 500ppm depending on the molecule and structure. In a majority of flourinated organic compounds, the chemical shift ranges from 100 to -250ppm. F19 also has strong homonuclear (among adjacent F19 nuclei) and heteronuclear (to H1, C13, etc.) J-couplings. Note the following when setting up a F19 experiment:


Choose one of the following (among others) to reference your F19 spectrum:

  1. For most accurate and convenient chemical shift referencing, use TMS at < 1% as an internal 0.0ppm reference for H1. F19 is indirectly referenced relative to the TMS H1 peak accordingly to IUPAC standard.
  2. Alternatively, for rough referencing, type setref to use the lock signal to reference any nucleus in the direct dimension. Note the setref command needs solvent to be set correctly and locked. See this page for more details.
  3. If locking is not possible, use neat CFCl3 as an external reference at 0.0ppm and run experiment unlocked.

Procedure for H1 coupled F19 experiment on nmr500

Step 1: Optional: Collect and reference H1 spectrum

Step 2: Optional: Estimate F19 transmitter offset to use (Skip this step if you do not know what ppm range your F19 signals cover)

Step 3: Change F19 filter and tune probe

Step 4: Set up F19 experiment

Default parameters

Step 5: Collect final spectrum

Step 6: Processing

Step 7: Recable and tune probe back for H1

How to scan through the entire F19 shift range in an arrayed experiment


  • Sample: Lufenuron ~20mg/mL in CDCL3
  • Data collected in Dec 2010

  • Chemical shifts assigned, from left to right in structure, based on a F19 chemical shift table and integral ratios are:
  • CF3: -75ppm
  • CF: -210.5ppm
  • CF2: -78 and -79 ppm
  • CF/CF in ring: -110ppm



1: spectrum with sw=500000 centered at -201 ppm. Note the baseline rolling and phase abnormality due to the large bandwidth and pulse offset effect. F19 wide
2: spectrum with sw=500000 centered at 0 ppm. Compare with 1 and note the F19 peak at -211ppm did not get excited and is missing from the spectrum due to the large offset from transmitter center. Also note the changes in relative intensity of the peaks from 1. F19 wide
3: Narrow down spectral window with movesw to enclose all peaks found in 1 and recollect data (nt=4). Note baseline rolling due to large 1st order phase correction. F19 narrow
4: Apply baseline correction with bc command F19 narrow bc
5:Following 4, reset integrals and scale integral of peak at -110ppm to 2. The integral for each multiplet from left to right, is: 2.7, 0.92, 0.90, 2.0, and 0.79. F19 narrow bc int
6: Window size is further cut down to only include the four peaks on the left with transmitter centered at -92.5ppm. The integrals for the multiplets from left to right, are: 2.97, 1.02, 1.02, 2.0. These values are much more accurate than in 5. F19 narrow bc int

H. Zhou updated Dec 2010