Stabilization of even-electron ions in 4-amino-substituted cytosines. Appearance of the strong ortho effect between an aryl substituent and the pyrimidinyl ring

The mass fragmentation of 4-arylaminocytosine derivatives was investigated and it was found that the ortho effect is mainly responsible for the strong stabilization of even-electron ions formed during fragmentation. The ortho effect in this class of compounds completely eliminates other possible fragmentation patterns. This effect disappears when the aryl substituent is separated from the 4-amino group of the cytosine moiety by a methylene group.