Mass spectra of 5,10‐dihydrophenarsazines, 5,10‐dihydrophenarsazine and phenophosphazine oxides, and related heterocycles

The electron‐impact‐induced fragmentation of eight 5,10‐dihydrophenarsazines and three 5,10‐dihydrophenarsazine oxides proceeds by loss of the exo cyclic arsenic substituents to give the stable ion (II) as the base peak followed by loss of arsenic to give a carbazole species (III). The fragmentation pattern is independent of substituents at either hetero‐atom in the cases examined. Dihydrophenophosphazine oxides behave similarly but give as the base peak an ion in which the phosphoryl grouping is retained. 10,11‐Dihydro‐5‐phenyl‐5H‐dibenzo[b, f][1,4]azarsepine and 2,3‐dihydro‐1,2‐diphenyl‐1H‐benz [c]azarsole fragment by different pathways. It is suggested that the ability of arsenic and phosphorus to sustain a positive charge by d π‐ p π bonding is the dominating factor in these fragmentations.