Characterization of gem-difluoropropargyl synthons through HF loss from protonated molecules in methane chemical ionization mass spectra

Electron impact and methane chemical ionization mass spectra were obtained following gas chromatography/mass spectrometry for several gem-difluoropropargyl compounds, which had been synthesized as potential intermediates for synthesis of gem-difluoromethylene-containing C-3 acetylenes. EI spectra were variable with respect to the presentation of molecular ions, depending on substituent functional groups present. Methane-CI spectra were characterized by loss of 19 mass units from molecular weight with all compounds examined. These M − 19]⁺ ions often presented as base peaks of the CI spectra, and were more reliably present and abundant than M + 1]⁺ ions for these compounds. These ions could have been formed by elimination of HF from the protonated molecules under conditions of methane chemical ionization.