STEREOCHEMICAL EFFECTS IN THE MASS-SPECTRA OF -ARYL-4A,5,6,7,8,8A-HEXAHYDROQUINAZOLIN-4(3H)-ONES AND -ARYL-4A,5,6,7,8,8A-HEXAHYDROQUINAZOLIN-4(3H)-ONES

The electron-impact (EI) and collision-induced dissociation (CID) spec tra of the title compounds were studied, The main fragmentation routes of M(+.) ions included losses of hydrocarbon species and the formatio n of ArCNH+ cations, The geometry of ring annelation predictably affec ted the stabilities of the molecular ions and the relative abundances of some characteristic fragment ions, The abundance ratios [M-H](+)/M( +.), which were higher for trans-annelated isomers, correlated with th e electronic effects of aromatic ring substituents, Molecular ions and [M-H](+) ions of stereoisomers gave different CID spectra, suggesting that stereochemical differences are still preserved after the loss of hydrogen from M(+.) ions, The stereochemical effects in the EI spectr a were more pronounced at lower impact energies (16-24 eV), Several cr iteria for differentiating cis- and trans-annelated isomers based on t he relative abundances of characteristic fragment ions were establishe d.