Effect of torsional motion on the 13C, 1H and 19F NMR chemical shifts in 2,2′-difluorobiphenyl

Abstract

Abstract Contribution of inter-ring torsional motion of 2,2′-difluorobiphenyl (DFBPh) to the NMR chemical shifts (CSs) and lineshapes is investigated using B3LYP/aug-cc-PVDZ computations. The anharmonic potential energy curve for this vibrational motion is calculated by a relaxed scan over the whole span of its coordinate, inter-ring dihedral angle D. The NMR CS curves for the most affected 1H, 13C and 19F nuclei are calculated as functions of D for these relaxed structures using IGAIM method. Lineshapes arising from the unaveraged NMR CSs are simulated for each vibrational state, and their corresponding state averages and the thermally averaged values at two temperatures are calculated. Lineshape broadening in slow regime is significant especially for the 19F nuclei. The averaged CSs differ slightly, but detectably, from their corresponding equilibrium values. It is thus concluded that for accurate evaluation of the NMR CSs and experimentally compatible NMR spectra, such vibrational analysis is necessary.