Strained heterocyclic systems. VII. The mass spectral fragmentations of dihydrocycloalka[b]quinolines and quinoline N-Oxides

High resolution mass spectra of compounds 1-6 were investigated. The quinolines ( 1-3 ) all exhibit a prominent (M-1)⁺ peak and subsequent loss of HCN. These processes are consistent with azatropylium ion intermediates. The N-oxides ( 4-6 ) all exhibit major peaks at (M-16)⁺; the abundance of the latter is related to the geometry of the molecule. The four-membered ring compounds (3 and 6) give more complex spectra, which reflect the influence of the fused strained ring.