Carbon‐13 NMR of tertiary fluorosteroids as a stereochemical probe

The 13C NMR spectra of tertiary fluorinated steroids possessing no functional groups in the vicinity of the fluorine have been measured. All α‐ and β‐carbons are deshielded by the fluorine atom. The γ‐carbons, however, are divided into two groups. The carbons gauche to the fluorine atom are all shielded by 1–8 ppm, whereas the γ‐carbons anti to the halogen are all deshielded by 2–5 ppm. Apart from the α‐Carbons, which have coupling constants of 170–180 Hz, all β‐Carbons are also coupled to the fluorine with a 2J(CF) value of approximately 20 Hz. The γ‐carbons gauche to the fluorine have a very small coupling constant (usually 0‐3 Hz), while the anti γ‐carbons are split by the fluorine by 6–8 Hz. Both chemical shifts and coupling constants can be used for the Stereochemical evaluation of fluorosteroids.