- The mass spectra of (E,E)-α,α′-dibenzylidenecyclopentanone, -hexanone, -heptanone, and (E)-2-benzylidene-1-tetralone are reported. The main feature in these spectra is E-Z isomerization of the parent ions followed by production of stable benzopyrilium ions. A competing but less important fragmentation mode involves α-cleavage and CO extrusion as initial steps. The latter route dominates in the mass spectrum of (E,E)-3,5-dibenzylidenetetrahydro-4H-pyran-4-one. The mass spectrum of (E,E)-3,7-dibenzylidenecycloheptane-1,2-dione differs from that of the lower cyclohexanone derivative only by M and M - CO ions. At 70 eV benzopyrilium ion formation is virtually independent of the electronic nature of the benzylidene moieties, but is promoted by electron-donating groups and reduced by electron-attracting substituents attached to the fused aromatic ring in 2-arylidene-1-tetralones.