600 MHz 13C NMR ? how come ?

Hi all ,

prof. Gordon, the signal is not buried under noise ,I did  from 250 to 1000 repetition.

prof. Michael, Thank you for your suggestion. The instrument is NMR 600MHz, The spectrum was collected at 100MHZ.

Mis . Xu , The instrument is NMR 600MHz. The spectrum was collected at 100MHZ.

Thank you all for your reply .

I agree with Michael Päch and Gorden W. Driver. The carbons bounded to boron (NMR active nucleus) in alpha and beta position, both have a high coupling to the boron (1J and 2J) therefore you get a multiplett because 11B (81% abundance) has a spin of 3/2 and 10B (19% abundance). Also the fluor-atoms (2J) make a quartet-multiplet with the alpha 13C-carbon with about 20Hz. In a normal 13C-spectra with power-decoupling you don't get a NOE-enhancement from the protons and therefore the signal is weak. To see the multiplett you need much more scans.

Thank you all

Please check out 1H, 13C, 19F and 11B NMR spectral reference  data of some potassium organotrifluoroborates by Roberta Oliviera, et al. (abailable on RG), also on the Net (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2907063/table/T2/. The full text gives NMR spectral data for 28 potassium organotrifluoroborates. For potassium phenylethynyl trifluoroborate, the 13C shifts are given as 130.9;128.3;126.9;125.4;104.3 (br.); 89.5 (solvent DMSO-d6). Typical pulse angle for 13C was 90deg, delay 2.3sec, AT=1.7s, 1024 repetitions, SW=250ppm.

Yes, try a longer run.

If you have adiabatic decoupling techniques (for simultaneously broadband decoupling 1H and 19F), or at least decoupling 19F, you might also get a simpler spectrum. The ethinyl carbons, not having attached H's, will not benefit from 1H broadband decoupling, as pointed out by several responders.