| Abstract: | Mass spectra of steroids containing a carbonyl group in position 11 and a 3α-hydroxy group in a cis connected A/B ring system are characterised by very strong M – 72]+· key ions and may therefore be clearly differentiated from the spectra of their isomers. The mechanism of this fragmentation reaction was investigated by deuterium labelling and the DADI technique. The 3α-hydroxy group is eliminated together with the 9α-H atom. Next a hydrogen atom is transferred from the A ring to the B/C/D ring system. This causes the cleavage of the C-3? C-4 bond and expulsion of C atoms 1 to 4 as butadiene. In 3α-hydroxy-5α-androstanes possessing no 11-keto group an analogous M – 18]+. fragment is fromed, followed by the elimination of ethylene originating mostly from C-1 and C-2. |
