The optimal DFT approach in DP4 NMR structure analysis - pushing the limits of relative configuration elucidation

What computational methods should be used to achieve the most reliable result in computational structure elucidation? A study on the effect of quality and quantity of geometries on computational NMR structure elucidation performance is reported. Semi-empirical, HF and DFT methods were explored, and B3LYP optimized geometries in combination with mPW1PW91 shifts and M06-2X conformer energies was found to be best. The required number of conformers considered has also been investigated, as well as several methods for the reduction of this number. Clear guidelines for the best computational NMR structure elucidation methods for different levels of available computing power are provided.