E. Borkowski, F. Suvire, R. Enriz
Aug 15, 2010
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Influential Citations
13
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Journal
Journal of Molecular Structure-theochem
Abstract
Abstract The 13 C chemical shifts of 15 pentacyclic terpenoids (fernenes) are compared to predicted 13 C NMR chemical shifts obtained via empirically scaled GIAO shieldings. We report that accurate (rms error approx. 1.5 ppm) predictions of 13 C chemical shifts can be achieved for these fernenes through the use of scaled shieldings calculated from GIAO theory with a relatively small basis set and on the basis of geometries obtained from DFT calculations. The best results (considering a reasonable cost-to-benefit ratio) were obtained from B3LYP/6-31G(d)//B3LYP/6-31G(d) computations. The chemical shifts anisotropy asymmetry ( η was included in our calculations, enhancing the correlations between calculated and experimental chemical shifts. Our results indicate that the inclusion of a scaling factor allow to obtain an excellent correlation between δ calc and δ exp . Also, the inclusion of asymmetry improves this correlation. In addition, taking into account the different conformations and the solvent effects a slight enhancement was obtained in this case.