The mass spectra of 13C labelled methylene derivatives of steroids--IV

The mass spectra of the 3-ethylene ketal of delta 5-pregnan[20-13C]methylene-3-one and 17 beta-acetoxyl[3-13C]methyleneandrost-1-ene have been examined. In both cases there are some fragments which show either relatively large retention or elimination of 13C label and these can be assigned to some fragmentation paths which generally follow those found for diterpenic and steroidal hydrocarbons, and are in good agreement with the empirical fragmentations rules in mass spectrometry.