19-Fluorine nuclear magnetic resonance chemical shift variability in trifluoroacetyl species

Abstract

This review examines the variability of chemical shifts observed in 19-fluorine (19 F) nuclear magnetic resonance spectra for the trifluoroacetyl (TFA) functional group. The range of 19 F chemical shifts reported spectra for the TFA group varies generally from −85 to −67 ppm relative to CFCl3 . The literature revealed several factors that impact chemical shifts of the TFA moiety − substrate topology, electronic environment, solvent polarity, and concentration effects. Often these effects conspire to cause deshielding of the TFA group by up to 15 ppm. These factors will be examined for a series of TFA-functionalized acyclic, cyclic, aromatic, and heterocyclic molecules.