Electrospray ionization–tandem mass spectrometric study of fused nitrogen‐containing ring systems

Four fused nitrogen‐containing ring systems were investigated by electrospray ionization–tandem mass spectrometry: Pyridazino‐indoles, pyridazino‐quinolines, a pyrimido‐quinoline derivative and pyrimido‐cinnolines. Fragmentation patterns of these compounds are discussed and compared. Several characteristic cross‐ring fragments were formed mainly on the pyridazine and pyrimidine rings of the ring systems. The connected Cl, NO(2), Me, Ph and more extended heterocyclic substituents influenced the fragmentation.