Hydrogen transfer-induced S-C rearrangement in the molecular ion of thioanisole derivatives with site-specificity

In this study, the gas-phase fragmentations of molecular ions of thioanisole derivatives were investigated using electron ionization mass spectrometry (EI-MS). In the EI-MS spectrum, a characteristic fragment ion [M - SH]⁺ was observed. The same result with the molecular ion of 3-aminothioanisole was enhanced, while the same phenomenon was not obvious in the EI-MS spectra of 2- or 4-aminothioanisole. To explain the fragmentation, we proposed a mechanism that involved the hydrogen transfer-induced S-C rearrangement with 3 pathways. Substituent effect results, deuterium-labelled experiments and density functional theory (DFT) calculations also confirmed the proposed mechanism.