Effects of fluorine bonding and nonbonding interactions on 19F chemical shifts

F-19-NMR signals are sensitive to local electrostatic fields and are useful in probing protein structures and dynamics. Here, we used chemically identical ortho-F nuclei in N-phenyl gamma-lactams to investigate the relationship between F-19 NMR chemical shifts and local environments. By varying the structures at the C5- and C7-substituents, we demonstrated that F-19 shifts and Hammett coefficients in Hammett plots follow typical relationships in bonding interactions, while manifesting reverse correlations in nonbonding contacts. Quantum mechanics calculations revealed that one of the ortho-F nuclei engages in n -> pi* orbital delocalization between F lone pair electrons (n) and a C - O/ArN antibonding orbital (pi*), and the other ortho-F nucleus exhibits n ? sigma orbital polarization between the n electrons and the C-H sigma bonding orbital. As F-19 NMR spectroscopy find increasing use in molecular sensors and biological sciences, our findings are valuable for designing sensitive probes, elucidating molecular structures, and quantifying analytes.