13C19F spin–spin coupling in some monofluoro‐substituted polycyclic aromatic hydrocarbons

Abstract

AbstractThe determination and complete assignment of the 13C19F coupling constants and 13C chemical shifts for 15 monofluoro derivatives of nine polycyclic aromatic hydrocarbons are reported. Fluorine substitutent effects on the 13C chemical shifts are given and their regular behaviour, making comparisons between different compounds possible, is discussed. The numerical values of the 13C19F long range coupling constants are found, with a few exceptions, to decrease in an alternating manner along the periphery of the molecules. In several cases the signs of the coupling constants have been determined. It appears that the signs alternate, but additional evidence is required. The magnitudes of different types of coupling constants are discussed in terms of steric and electronic effects. CNDO/2 and INDO calculations of the 13C19F coupling constants in the fluoronaphthalenes have been performed using the ‘sum‐over‐states’ method with the aim of examining the orbital and spin–dipole contributions to the various couplings.