Effect of intramolecular conjugation on the primary fragmentation in EI mass spectrum of 2-allenylthio-1H-pyrrole derivative

The anomalous primary fragmentation (no C–S bond cleavage) in the electron-ionization (70 eV) mass spectrum of 1-isopropyl-3-methoxy-2-(propa-1,2-dien-1-ylthio)-1H- pyrrole is considered in terms of intramolecular electronic effect. The calculation of the geometry (B3PW91/6-311G**) and the study of electron density delocalization (NBO) revealed the effect of electron density transfer LpS → π* (from the lone pair of sulfur atom to the π-system of allene double bond) on primary fragmentation pathways.