Mass Spectra of New Heterocycles. XVII. Main Fragmentation Routes of Molecular Ions of 4-Alkoxy-5-amino-3-methylthiophene-2-carbonitriles under Electron and Chemical Ionization

For the first time decomposition was investigated of 4-alkoxy-5-amino-3-methylthiophene-2-carbonitriles under the conditions of electronic (70 eV) and chemical (reagent gas methane) ionization. At the electronic ionization the compounds under study except for 4-(1-ethoxyethoxy) and 4-(ferrocenylmethoxy) derivatives] form stable molecular ions that decompose mainly by the cleavage of an alkyl radical from the alkoxy-substituent. Further fragmentation of the arising ion M–Alk]⁺ depends on the substituent nature in the amino group. In the mass spectrum of 4-(ferrocenylmethoxy)-substituted thiophene peaks of the ion FcCH₂]⁺ and its fragmentation products prevail. In the mass spectra of chemical ionization predominant peaks belong to ions M^+·, M + H]⁺ and M + C₂H₅]⁺, and fragment ions are absent.