The shielding effect of fluoroaromatic rings in NMR

• Evaluation of the shielding effect of fluoroaromatics by nucleus-independent chemical shift (NICS) technique.
• Calculations of NICS values at more than 3.5 Å above the aromatic ring.
• Correlation of chemical shifts between theoretical and experimental values.

The shielding effect of fluoroaromatics on nuclei was estimated using nucleus-independent chemical shift (NICS) calculations at the GIAO/B3LYP/6-311++G(2d,p) level. The strengths of diamagnetic contributions of hexafluorobenzene at more than 3.5 Å above the ring center were estimated to be ca. 0.73 times those of benzene. The chemical shift of a proton located above the fluoroaromatic ring is shifted upfield owing to such a relatively weak shielding effect of fluoroaromatic; we demonstrated that in 1H NMR measurement on BINAP bearing C6F5 groups.

The shielding effect of fluoroaromatics in NMR was studied using nucleus-independent chemical shift (NICS). The upfield shift of the proton in 1H NMR due to the shielding effect of the adjacent C6F5 group was also demonstrated experimentally and theoretically.Figure optionsDownload as PowerPoint slide