Transmission mechanisms of inter‐proton long‐range couplings in substituted anisoles

Inter‐proton long‐range and ring couplings were measured in o‐anisaldehyde and in seven disubstituted anisoles. In order to investigate the transmission mechanisms of long‐range couplings with the methoxy group, partially restricted molecular orbital (PRMO) calculations were carried out within the FPT‐INDO method on o‐anisaldehyde. σ‐ and π‐electron, and through‐space transmitted components were separated. For the energetically favoured trans‐OMe conformation a through‐space component was found for the couplings of the methyl protons with the ortho‐proton, and it was found that its sign, as well as its magnitude, depends on their relative positions. If free rotation, however, is assumed for the methyl group, the averaged value for this coupling constant is negative.