THEORY OF NMR CHEMICAL SHIFTS IN AROMATIC FLUORINE COMPOUNDS

Abstract

Ramsey’s equation for the NMR screening constant is analyzed using an ASMO ground state wave function. It is shown that for aromatic fluorine compounds only the charge density at the fluorine atom and in the carbon-fluorine bund contribute significantly to the screening constant. Using the assumption that the important changes upon substitution in the meta or para positions occur in the \emph{pi}-electron system, the chemical shift is derived to be a linear function of the changes in the fluorine \emph{pi}-electron charge density and in the carbon-fluorine \emph{pi}-electron bond order. The fluorine \emph{pi} charge density term is controlled by the fluorine \emph{sigma} charge density and the carbon-fluorine \emph{sigma} bond orders; the \emph{pi} bond order term is controlled by the fluorine \emph{sigma} charge density.