DFT calculations of the 1H chemical shifts and 13C chemical shift tensors of retinal isomers

Abstract

An ab initio study on the accuracy of the prediction of 13C isotropic chemical shifts and nuclear magnetic shielding tensors of several geometric isomers of retinal within the density functional theory framework at the B3LYP/6-31G level is presented. In addition, the accuracy of the calculated 1H chemical shifts of the vinyl protons is investigated. The results are compared with available experimental data from solution and solid-state NMR. The calculated 13C isotropic chemical shifts in the conjugated chain of the retinal isomers are in reasonable agreement with the experiment with a rms error of 4.1 ppm and a correlation coefficient ρ=0.982. For the calculated 1H isotropic chemical shifts of the vinyl protons, the overall rms error is 0.5 ppm and the correlation coefficient is ρ=0.993. We conclude that, even with a small basis set, density functional theory provides a valuable tool in the prediction of 13C NMR properties. A larger basis set is recommended to predict 1H chemical shifts.