Electron impact (EI) pos. ion mass spectra of 37 fluorinated phosphonium and arsonium ylides, and the pos. and neg. ion chem. ionization (CI) mass spectra of 8 fluorinated arsonium ylides Ph3As+C-(COR1)COR2 (R1 = Me, Ph, MeO; R2 = fluoroalkyl), using methane as the reagent gas, were reported. Fragmentation patterns have been discussed. The cleavage mechanism of EI mass spectra of fluorinated arsonium ylides is similar to that of fluorinated phosphonium ones. In pos. ion CI mass spectra of fluorinated arsonium ylides, ions [M + H]+, [(C6H5)3As + H]+, (C6H5)2As+, [M - R1]+, and [M - R2]+ are formed. Peaks such as [(C6H5)3AsO + H]+ and (C6H5)3As+F have been observed, indicating the migration of oxygen and fluorine from carbon to arsenic. The neg. ion CI mass spectra of fluorinated arsonium ylides are characterized by base peaks corresponding to loss of Ph radical.

Key words: MASS SPECTROGRAPHY, PHOSPHINE, ORGANO FLUORINE COMPOUNDS, ARSINE, YLIDE