The Relationship between 19F Substituent Chemical Shifts and Electron Densities: meta- and para-Substituted Benzoyl Fluorides

Article abstract of DOI:10.1002/mrc.1270140308

The 19F substituent chemical shifts (SCS) of meta- and para-benzoyl fluorides are found to correlate well with substituent parameters using the dual substituent parameter (DSP) equation, indicating that they reflect electronic perturbations induced by the substituent.The direction of the SCS values is such that donating substituents cause upfield shifts whilst acceptors cause downfield shifts.STO-3G calculations indicate that substituents induce only very small changes in ?-electron density about the fluorine atom, but that these changes correlate reasonably well with the observed SCS values.For the para series, the slope of the relationship between Δq_?^F and 19F SCS is 5000 ppm/electron, indicating the great sensitivity of the fluorine atom to small changes in electron density.