Mass spectra of twenty four silatranes were studied in detail using high resolution mass spectrometry and metastable ion measurements. The stability of molecular ion, the mode of formation of the base peak and the number of tragment ions depend mainly upon the property of substituent group. The fragmentation of silatrane under electron impact can take the following three routes: (1) the cleavage of the Si-R bond to produce a highly stable ion (M-R)+; (2) the ring fragmentation with the lose of the fragment C2H3O; (3) openning of one of the ring followed by the loss of CH2O or CH3O. The fragmentation mechanisms were discussed in terms of charge radical localization.

Key words: MASS SPECTROGRAPHY, NITROGEN HETEROCYCLICS, OXYGEN HETEROCYCLICS, SILICON HETEROCYCLICS COMPOUNDS, SILATRANE