cleavage of phosphorus rings cleavage of 1,2,4-triazinone rings 1,2,3-diazaphosphete 3-methylazet-2(1H)-oneMass fragmentation of cyclic alpha-aminophosphonate monoester containing 1,2,4-triazinone moiety i ii Abstract The electron impact induced fragmentation reactions The 1,2,4-triazine rings are rather stable relative to the phosphorus rings. Therefore, fragmentation of the phosphorus rings is more favorable for the compounds than the stable 1,2,4-triazine rings.