Mass spectrometry of aryl substituted di‐ and trisiloxanes

The mass spectra of arylpentamethyldisiloxanes, sym‐diaryltetramethyldisiloxanes and 1,5‐diaryl‐1,1,3,3,5,5‐hexamethyltrisiloxanes were examined. Isotopic labeling and peak matching were used to substantiate the proposed fragmentation mechanisms. Siliconium ions dominate the spectra. Loss of neutral fragments from the [M‐15]+ ions is important. Phenylpentamethyldisiloxane, sym‐tetramethyldiphenyldisiloxane and 1,1,3,3,5,5‐hexamethyl‐1,5‐diphenyltrisiloxane are representative examples of the three classes of compounds discussed. The [M‐15]+ ion of phenylpentamethyldisiloxane loses methane, dimethylsilanone [(CH3)2SiO] and phenylmethylsilanone [PhCH3SiO] to yield daughter siliconium ions. The [M‐15]+ ion of sym‐tetramethyldiphenyldisiloxane loses benzene, methane, dimethylsilanone and phenylmethylsilanone to yield daughter siliconium ions. The [M‐15]+ ion of 1,1,3,3,5,5‐hexamethyl‐1,5‐diphenyltrisiloxane loses benzene, tetramethylcyclodisiloxane and phenyltrimethylcyclodisiloxane to yield daughter siliconium ions. Finally, doubly charged ions are important in the mass spectra of the three series of aryl substituted di‐ and trisiloxanes discussed.