Electronegativity and linear electric field effect on γ-anti 13C chemical shifts

The contribution from the existence of a 1,3-diaxial H-α ?H-γ arrangement to the γ-anti effects of substituents X, which was previously believed to be generally shielding, is shown to be extremely dependent on the electronegativity of substituent X. In the presence of axial γ-substituents Y, linear electric field effects appear to play a significant role if the C-γ—Y bond is highly polarizable.