Calculating nuclear magnetic resonance shieldings using systematic molecular fragmentation by annihilation.

ABSTRACT

SMFA was used to calculate NMR shieldings in a test set of 15 molecules. Level 4 fragments were found to yield satisfactory results when hydrogen bonding was included in the calculations. The utility of additional long range corrections was also investigated. It was found that with hydrogen bonding already included, ab initio long range corrections were not necessary. Instead, inclusion of the McConnell correction for fragments was found to be sufficient. With these parameters the algorithm produces MADs of 0.046, 0.26, 0.24 and 1.04 ppm for hydrogens, carbons, nitrogens and oxygens respectively.