NMR vs. molecular modelling. Part III—a DFT-GIAO study of a series of 2-X-fluorobenzenes

The isotropic magnetic shielding [σIMS (ppm)] for a series of 2-X-fluorobenzenes was determined using the GIAO method and the BPW91/6–311G** basis set. Structures were optimized at the BPW91/6–31G* level. Fluorine chemical shifts were determined from a plot of the σIMS vs. the experimental shifts; and 13C chemical shifts were determined by substraction of the various σIMS from that for TMS. Carbons with attached heteroatoms exhibited larger errors than unsubstituted carbons, suggesting that augmentation to higher basis sets might be appropriate for these carbons.