The shielding effect of fluoroaromatic rings in NMR

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 إ 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.