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

An ab initio study on the accuracy of the prediction of C-13 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 H-1 chemical shifts of the vinyl protons is investigated. The results are compared with available experimental data from solution and solid-state NMR. The calculated C-13 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 rho = 0.982. For the calculated H-1 isotropic chemical shifts of the vinyl protons, the overall rms error is 0.5 ppm and the correlation coefficient is rho = 0.993. We conclude that, even with a small basis set, density functional theory provides a valuable tool in the prediction of C-13 NMR properties. A larger basis set is recommended to predict H-1 chemical shifts. (C) 2004 Elsevier B.V. All rights reserved.