Mass spectral fragmentation pathways of propranolol related beta-fluorinated amines studied by electrospray and electron impact ionization

Propranolol, its 1"-mono-, di-, and trifluorinated analogs, and other relat ed compounds were analyzed under electrospray ionization ion trap collision -induced dissociation (ESI-CID) and electron impact (EI) conditions. Intere sting trends were observed in the fragment ions formed in both cases. Under ESI conditions, the abundances of product ions easily explained by protona tion on the amine nitrogen decreased relative to the abundances of those fo rmed from the ether-protonated species as the number of fluorines increased from zero to three. Under EI conditions, the distribution of fragment ions was shifted away from those arising from a nitrogen-centered cation radica l and toward those arising from an ether oxygen-centered cation radical, Th e changes observed in apparent molecular sites of protonation and of ion ra dical formation in the mass spectra are consistent with the electron-withdr awing effects of the sequentially added fluorines, These effects are correl ated with changes in solution phase pK(a)'s of the fluorinated amines, Copy right (C) 1999 John Wiley & Sons, Ltd.