Substituent shielding parameters of fluorine‐19 NMR on polyfluoroaromatic compounds dissolved in dimethyl sulphoxide‐d6

Abstract

AbstractHigh resolution fluorine‐19 NMR spectra of polyfluoroaromatic compounds dissolved in deuterated dimethyl sulphoxide were measured and substituent shielding parameters were derived. These parameters were compared with the values observed in deuterated chloroform solutions and used to identify fluoroaromatic compounds related to perfluorinated polyimides and poly(amic acids)s. Average differences of Δδ between the solvents are 1.1, 1.0 and 2.1 ppm for o‐, m‐ and p‐fluorines of monosubstituted pentafluorobenzenes, respectively. The significant difference for p‐fluorine of NH2 is important in identifying perfluorinated diamines because they are source materials for perfluorinated polyimides. Substituent shielding parameters for meta and para substitution increase as the respective Hammett σ constants increase, which indicates that fluorine‐19 NMR chemical shift is primarily determined by electron density.