The mass spectra of some tris(trimethylsilyl)acylsilanes and tris(trimethylsilyl)silanes

While tris(trimethylsilyl) alkanoylsilanes fragment in the acylsilane form yielding [(Me 3 Si) 3 SiCO] + by α‐cleavage, the molecular ions of their aryl counterparts rearrange to ionized silaethenes prior to cleavage, paralleling known photochemical behaviour. Sila‐allyl type structures are attributed to the stable [MMe˙] + ions obtained by subsequent cleavage. Metastable ion characteristics reveal the identity of the structures of the monomeric silaethene ions obtained from one of the aroylsilanes and a 1,2‐disilacyclobutane. The non‐compliance of the alkanoylsilanes with their photochemical behaviour is attributed to a preferred elimination of the stable alkyl radical (R˙) from the molecular ions. Several polysilanes display abundant odd‐electron ions which may possess a disilene structure.