Electron-impact fragmentation of cyclocarbosiloxanes

The fragmentation of six and eight membered methyl substituted cyclocarbosiloxanes of general formula (CH3)6Si3O3  n(CH2)n (n = 1 or 2) and (CH3)8 Si4O4−n(CH2)n (n = 1, 2 or 3) under electron-impact (70 eV) is reported. The behaviour of these compounds under electron-impact is intermediate between that of the corresponding cyclosiloxanes and cyclocarbosilanes. In every case the most intense singly and doubly charged ions correspond to the loss of one and two methyl groups respectively. In going from the cyclosiloxanes to the cyclocarbosilanes the intensity of the primary ions is reduced and the intensity of those fragment ions whose formation involves the rearrangement or breakdown of the cyclic framework of the molecule is increased. These ions are the [M CH3(CH3)4Si]+ ions in the eight membered and the [(CH3)3Si]+ ions in both cases. The data on doubly charged and metastable ions in the mass spectra of the cyclocarbosiloxanes are presented and discussed. The fragmentation of six and eight membered methyl substituted cyclocarbosiloxanes of general formula (CH3)6Si3O3  n(CH2)n (n = 1 or 2) and (CH3)8 Si4O4−n(CH2)n (n = 1, 2 or 3) under electron-impact (70 eV) is reported. The behaviour of these compounds under electron-impact is intermediate between that of the corresponding cyclosiloxanes and cyclocarbosilanes. In every case the most intense singly and doubly charged ions correspond to the loss of one and two methyl groups respectively. In going from the cyclosiloxanes to the cyclocarbosilanes the intensity of the primary ions is reduced and the intensity of those fragment ions whose formation involves the rearrangement or breakdown of the cyclic framework of the molecule is increased. These ions are the [M  CH3(CH3)4Si]+ ions in the eight membered and the [(CH3)3Si]+ ions in both cases. The data on doubly charged and metastable ions in the mass spectra of the cyclocarbosiloxanes are presented and discussed.