Gas chromatography mass spectrometry of the stereoisomers of heterocyclic compounds. Part 2a. Perhydroxanthenes

The importance of GC-data for the structural elucidation of novel isomers by GC-MS is discussed. A gas chromatographic-mass spectrometric study of mixtures of the stereoisomers of perhydroxanthene (PHX) has been carried out. Separation has been accomplished on a column packed with graphitized thermal carbon black (GTCB) and on a capillary column of high efficiency. In accordance with the mass spectral evidence together with the known cis-syn-cis, trans-anti-cis and trans-syn-trans isomers four novel stereoisomers have been found. Three of them, cis-anti-cis, trans-syn-cis and trans-anti-trans are theoretically expected, whereas the fourth novel isomer is surprising and has been preliminarily assigned as conformer B of cis-syn-cis PHX, The stereospecificity of the fragmentation of PHX isomers under electron impact appears almost suppressed by the predominant formation of a stable oxonium ion [M -C3H7](+). The similarity of the mass spectra complicates the structural elucidation of novel isomers based on the qualitative relationships between their retention on the column packed with GTCB and hypothetical molecular structures.