Abstract

Evaluation of Exchange-Correlation Functionals for Calculating 1H and 13C NMR Chemical Shifts of a Series of Lactones and Lactams in Solution

Nadia FASKA* and Fatima EL BAZ

Faculty of Applied Sciences Ait Melloul, University Ibn Zohr Agadir, MOROCCO. LCAPE, Department of Chemistry, Faculty of Sciences, University Ibn Zohr Agadir, MOROCCO.

ABSTRACT

Experimental and theoretical 1H and 13C NMR chemical shifts for a set of lactones and lactams were determined and analyzed. The theoretical NMR chemical shifts were calculated using density functional theory (DFT) and gauge independent atomic orbital (GIAO) approach in fourteen exchange-correlation functionals. The experimental versus computed chemical shift values for proton and carbon were compared and evaluated using linear correlation (R2), mean absolute error (MAE), mean squared error (MSE), and root mean squared error (RMSE) with respect to the relative ability of each functional to predicting 1H and 13C nuclear magnetic resonance spectra. For 13C NMR chemical shifts, statistical evaluation of data indicates that the most accurate prediction of 13C chemical shifts is achieved at B3PW91, wB97XD, and CAM-B3LYP functionals, although B3PW91 proved marginally superior to the others. For 1H shift data, the best results were obtained using the B3LYP, B3PW91, and MPW1PW91 functionals. The calculated results of 1H and 13C NMR chemical shifts for all the nuclei studied in the series of lactones and lactams are in good agreement with the experimental data.

Keywords :Chemical shifts, density functional theory, lactones, lactams, GIAO.