The use of partially restricted molecular orbitals to investigate transmission mechanisms of spin–spin coupling constants. III—an INDO study of long‐range FH couplings in fluorinated derivatives of toluene

Transmission mechanisms of long‐range FH couplings in several fluorinated derivatives of toluene are analysed carrying out partially restricted molecular orbital calculations at the INDO level of approximation. All π‐components follow the A+B sin2θ dependence, with the dihedral angle defined by the exocyclic CH (or CF) bond and the aromatic ring plane. Four‐ and five‐bond couplings show an important σ‐component, which follows the known zig‐zag rule. Both σ‐ and π‐contributions show a conspicuous insensitivity to fluorine ring substitution. Moreover, four‐bond couplings present an important through‐space component, which is negative for a cis arrangement. A sign inversion is found at a dihedral angle between 70° and 80°, which is interpreted as indicating that several through‐space mechanisms are operating.