¹³C nuclear magnetic resonance spectra. XV—the γ‐<i>anti</i> substituent effect and its dependence on substitution at the α‐ and γ‐carbon atom

Abstract

Abstract It is shown that the γ α effects of hetero substituents on the 13 C chemical shift (γ α SCS) are enlarged by +2 to +5 ppm by substituting the α‐hydrogen atom by any group or atom (e.g. CH 3 , OR, F, Cl, Br). The same is encountered when the axial γ‐hydrogen is replaced by CH 3 , OH or F. If, however, the substituting atom at the γ α ‐carbon atom is a higher‐row halogen (Cl or Br), diamagnetic γ α SCS for this signal are observed which may even exceed those for unsubstituted γ α ‐carbon atoms. The removal of a 1,3‐diaxial hydrogen‐hydrogen interaction and the existence of a still unspecified ‘heavy halogen effect’–both diamagnetic contributions to the γ γ SCS of hetero substituents–are responsible for these findings. Methyl groups do not behave like hetero substituents with respect to the γ α SCS.