INTRAMOLECULAR SCREENING EFFECTS ON NUCLEAR MAGNETIC RESONANCE CHEMICAL SHIFTS .3. SOME INVESTIGATIONS OF CORRELATION BETWEEN FLUORINE-19 NUCLEAR SCREENING AND INTRAMOLECULAR ELECTRIC FIELDS AND AN ASSIGNMENT OF 19F RESOANCE SPECTRUM OF PERFLUOROBICYCLO[2,2,1]HEPTANE

Perfluorobicyclo[2,2,1]heptane, trans-perfluorodecalin, and perfluorocyclohexane are taken as the basis for the investigation of methods for the correlation of fluorine-19 nuclear screening with intramolecular electric fields. The most satisfactory correlation is obtained by use of an equation of the form Δσ = -XΔEz - YΔ(E2) - ZΔ〈E2〉. The point of origin of the electric fields associated with C-F bonds is investigated, together with the validity of including contributions from C-C bonds to the 〈E2〉 term.