Mass spectrometric investigation of some α-trifluoromethyl-α-amino acids

The fast atom bombardment-induced mass spectrometric behaviour of four fluorinated α-amino acids was studied in detail with the aid of metastable ion studies and accurate mass measurements. Comparison with the behaviour of unfluorinated analogues suggests that the presence of fluorine makes the carbonylic oxygen the most prone to protonation. This hypothesis was confirmed by AM1 semiempirical calculations which indicate that the carbonylic oxygen of the carboxyl group exhibits, in the case of fluorinated compounds only, the highest proton affinity.