The structural dependence of the inductive effect. Part I. The calculation of geminal substituent effects upon fluorine-19 chemical shifts

We present a simple method of calculating the effects of geminal substituents upon the differences in shielding between 19F nuclei bonded to sp3 carbon in a variety of compounds. A single experimental parameter is used, the Huggins electronegativity of α-substituents. The method rationalises some hitherto puzzling data, and makes it possible to calculate the chemical shifts (referred to CFCl3 as an arbitrary standard) of 19F nuclei in a variety of molecules containing the elements C, H, N, O, F, Cl, Br, and I; the calculated values (in the absence of long-range interactions) agree with experimental results to within the errors dictated by solvent effects and referencing procedures.