I am trying to take Carbon NMR of one of my new compounds having pentaflurobenzene ring in it. If I run Carbon NMR I got Carbon for all carbon of compound but I dont get fluorinated Carbon of pentaflurobenzene . Is there any reason that for big size compound , fluoridated Carbon does not show up?
Basically, it shouldn't be a problem to detect these signals. (See attachments). However, if you have a large organic molecule with only one C6F5 present, you might lose the three patterns in the noise due to multiple (o,m,p) couplings (or there might not be present at all?).
https://www.google.hu/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0CEMQFjAF&url=http%3A%2F%2Fpubs.rsc.org%2Fen%2Fcontent%2Farticlelanding%2F1978%2Fp2%2Fp29780000855&ei=Pq0xVOCNGYjDOabZgNAH&usg=AFQjCNFjrERjwyF-tVsn_O88bKKqYX774Q&sig2=EZVWKogR-8hJpyQdYc1Q_w
If you have a TXI probe with 1H-X-19F, try a carbon proton-fluorine-decoupled.
If not, like Imre Tóth said, you will have multiple coupling that will decrease your signal intensity. Try your acquisition with a bigger relaxing time and so much scans... Like D1 = 4 and 16k scans or much.
Similarly you should read the previous Journal of Magnetic Resonance paper - The Complete 13C, 19F, 1H Spectral Analysis of the Flurobenzenes C6HnF6-n III. The remaining members of the series INDO MO Calculations of JFH, JFF, JCH and JCF. Journal of Magnetic Resonance V27(1), pp1-21 (1977).
Your spectra is spread out over many multiplets thus producing a relatively low SNR compared to other resonances. Also you are likely to have a significant T1 effect. You will need to account for that also. The shifted 1H spectra of your perflurorobenzene should still be detectable. You can use this as an INEPT probe to detect your C13 on the molecule.
The link for the above paper is included below.
http://www.sciencedirect.com/science/article/pii/0022236477901883
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