DFT analysis of rotational barriers, 1H and 13C NMR chemical shifts in neutral and protonated furfurylidenanilines

Abstract

Rotational barriers were calculated for 4′-substituted neutral and protonated furfurylidenanilines (FA) by DFT methods and the corresponding equilibrium geometries were identified. Neutral FA have equilibrium dihedral angle values sensitive to the substituent. 1H and 13C Substituent Induced Shifts in FA were calculated from shielding tensors and compared with experimental ones. The experimental trends in 1H and 13C Substituent Induced Shifts of these compounds are well reproduced by the calculations. Differences in Mulliken charges for each position in neutral and protonated furfurylidenanilines were correlated with experimental 1H and 13C Substituent Induced Shifts. The experimental trends in 1H and 13C Substituent Induced Shifts were well reproduced by charge differences. Only the functional group 1H shifts do not correlate with the charges reflecting the variable effect of the anisotropy term due to the benzene ring. Protonation of FA removes this variability.