Translational energy release and stereochemistry of steroids. IX‐The mechanism of the elimination of water from metastable ions in epimeric 3‐hydroxy steroids of the 5β‐series

Abstract

AbstractThe mechanism of water elimination from metastable molecular and [M − CH3˙]+ ions, as well as from ions deprived of ring D, in epimeric 3‐hydroxy steroids of the 5β‐series has been elucidated by deuterium labelling, by the measurements of the translational energy released during loss of water, and by collision‐induced decomposition mass‐analysed ion kinetic energy spectrometry. It was found that the dehydration of the metastable molecular ion in 3α‐hydroxy steroids of the 5β‐series occurs mostly regiospecifically as an elimination of the 3α‐hydroxyl together with the 9α‐hydrogen atom. The ring A in the molecular ion has to flip to the boat conformation to make this reaction possible. In the metastable molecular ion of 3β‐hydroxy steroids of the 5β‐series a different dehydration mechanism operates, with very little participation of the 9α‐hydrogen atom. The mechanisms of water loss from metastable [M − CH3˙]+ ions and from ions deprived of ring D differ from that of the molecular ion.