The determination of ring junction stereochemistry in steroids using mass-analysed ion kinetic energy spectrometry

The unimolecular mass-analysed ion kinetic energy (MIKE) spectra of 9 pairs of hydrocarbon and ketone steroid isomers, differing only in the stereochemistry at the A/B and C/D ring junctions, have been measured and are discussed with a view to unambiguous structural identification. Reproducible differences in the MIKE spectra are observed, which are large enough in certain instances to suggest that MIKE spectrometry may be used for determining the stereochemistry of the A/B and C/D ring junctions in steroidal isomers, even if the second isomer is not available. This fortunate situation is rarely observed in conventional mass spectrometry of stereoisomeric steroids. Furthermore, these differences in the MIKE spectra may be correlated with differences in strain energy between configurational isomers. The sensitivity of MIKE spectrometry to differences in strain energies makes it a potentially powerful stereochemical probe.