Evaluation of some density functional methods for the estimation of hydrogen and carbon chemical shifts of phosphoramidates

Abstract

1H and 13C NMR chemical shifts were measured for three phosphoramidates and computed using the B3LYP, WP04, TPSSh, M06-2X and wB97X-D density functionals. The experimental and computed chemical shifts for hydrogen and carbon were compared using linear correlation (R2), mean absolute error (MAE), root mean squared deviation (RMSD) and DP4 analysis. Applying a linear correction to the computed data improves the absolute accuracy and reduces random errors. For 13C NMR shift data, results from the GIAO/wB97X-D/cc-pVTZ/SCRF combination show the lowest value of RMSD (2.073). For 1H NMR shift data, CSGT/TPSSh/cc-pVTZ/SCRF shows RMSD of 0.070. The method that best applies to this class of compounds is CSGT/wB97X-D/cc-pVTZ/SCRF. DP4 analysis was used to correlate the chemical shifts (1H and 13C NMR) of the compounds and indicated that the method that best applies to this class of compounds is CSGT/wB97X-D/cc-pVTZ/SCRF, with DP4 analysis of 51.9%. In general, the best results were obtained when using implicit solvation model during calculations. The best method was applied on an external test set of 6 additional molecules and provided satisfactory results.