AbstractFragmentation upon electron impact of cinnoline(1)occurs with the consecutive loss of N2and C2H2. Fragmentation of 4,4′‐dicinnolyl(2)and 4‐styrylcinnoline(4)gives a series of ions leading to the “dibenzoladderene” ion(3)and the 1‐phenylbenzodibutylene ion(5)respectively. Fragmentation of 4‐styrylquinoline(6)also leads to5, but of more interest is the loss of H. during ring rearrangement to give the highly resonance stabilized 3‐styrylbenzocyclo‐pentadieneoneimine ion(7)which then loses N. Fragmentation of various other substituted cinnolines follow different pathways: 4‐methylcinnoline(8)apparently fragments through the “1,2‐diazatropylium” ion(9); nitrocinnolines fragment with initial loss of the nitro substituent; aminocinnolines fragment with initial loss of N2; and 4‐cinnolone(17)fragments with the consecutive loss of two HCN's and CO.The NMR spectra of cinnolines generally show the following order of deshielding: 3‐proton>8‐proton>4‐proton. The spectra of cinnolinum chloride(18)is interpreted in terms of protonation atN‐1 of1, and the spectrum of17is interpreted in terms of str