Mass spectra of methoxy-substituted 4-aminopyrimidines

In a study of the mass spectra of methoxy-substituted 4-aminopyrimidines it has been shown that in the molecular ion the positive charge is predominantly concentrated on the oxygen atom of the methoxy group, which explains the appearance of the fragmentary ions (M-H)⁺ and (M-CH₂O)⁺. In contrast to the halopyrimidines, the molecular ion does not exist in the imine form, which is characteristic only for the fragmentary ions (M-CH₂O)⁺.