Abstract Complete assignments of the 13C signals of diastereomeric 4, 5-epoxy-3-oxo steroids based on a combination of 1D and 2D NMR techniques are described The assignments were corroborated or corrected by calculation of the absolute isotropic 13C NMR shieldings using the Gauge Invariant Atomic Orbitals (GIAO) method at B3LYP/6-31+ G (d, p) level. Keywords: 4, 5-Epoxy-3-oxo-steroids, NMR, Absolute isotropic 13C NMR ...