PROXIMITY EFFECTS IN MASS-SPECTROMETRY - ELECTRON-IMPACT IONIZATION-INDUCED CYCLIZATION OF 1,2-BIS(1,4-DITHIAFULVEN-6-YL)BENZENES

The electron impact ionization mass spectra of o-, m- and p-bis(1,4-di thiafulven-6-yl)benzenes were studied by means of accurate mass measur ements, metastable analysis and collision-induced dissociation. Differ ences observed in the spectra of the ortho isomers are due to a cycliz ation reaction leading to molecular ions with the same structure as th ose generated from certain cyclic compounds, as confirmed by compariso n of linked scans at constant B/E of metastable and collisionally acti vated molecular ions. Parallels of this cyclization of molecular ions with their electrochemical or acid-induced isomerization are also disc ussed.