The chemical shifts of protons γ to a halogen atom in steroids

Abstract

The chemical shifts of protons γ to the halogen atoms in 3β-acetoxy-6β,19-epoxy-5α-halogenocholestane (IVb) and the 3β-hydroxy-derivatives (IVa; X = F, Cl, Br, or H) have been measured in dilute carbon tetrachloride solution. Dependence of chemical shift on the stereochemistry has been observed since the signal of one of the 19-methylene protons, which has a W stereochemistry with the halogen atom, shows a small increase in chemical shift with the electronegativity of the halogen atom whilst the other, broadened by long-range coupling with the 9α-proton, shows a downfield shift in the order Br = F > Cl > H and appears to be influenced more by anisotropy and field effects. The 3α-protons, which have a 1,3-diaxial stereochemistry, follow the order Br > Cl > F > H and appear to be mainly influenced by effects other than electronegativity.