The nature and fragmentation pathways of the molecular ions of some arylureas,arylthioureas, acetanilides,thioacetanilides and related compounds

Evidence as to the nature of the molecular ions of the title compounds near the ionization thresholds and of their fragmentation processes is presented and discussed. The mode of formation of 5-membered rings, involving the loss of an ortho substituent, is compared and contrasted with the formally similar process reported for the N-dimethyl N'-(o-X-phenyl) formamidines.