The fragmentation of 5-phenyl-1,4-benzodiazepin-2-ones. Mechanism for the formation of [M  H]

The fragmentations under electron impact of 5‐phenyl‐1,4‐benzodiazepin‐2‐ones are investigated with the aid of high resolution, metastable decompositions and deuterium labeling. Based on our data a mechanism for the formation of the [M – H]+ ion is proposed. It is shown that the [M – CHO]+ ion is probably formed by two different pathways. Data on two minor fragment ions give support to the structure proposed for the [M – CHO]+ ion.