Gauge invariant atomic orbital-density functional theory prediction of accurate gas phase 1H and 13C NMR chemical shifts

Hartree-Fock and density functional theory methods at gauge invariant atomic orbital approach with different simplest basis sets were employed for the computation of chemical shifts. The wave functions for calculating gas-phase 1H and 13C chemical shifts have been optimally selected using empirical models. The effects of electron correlation treatment, triple-xi valance shell, diffuse function, and polarization function on calculated chemical shifts have been discussed. Through empirical scaling of shielding, accurate predictions of 1H chemical shifts are achieved for the molecules studied, when considering small Pople basis sets. Gas phase experimental 1H chemical shifts in alcohols, amines and hydrocarbons were used to examine the theoretical optimal levels for obtaining the 1H chemical shift. In addition, this model has been used for 13C chemical shifts of gaseous hydrocarbons in relation to two different references. Furthermore, to assess the reliability of applied model for selection the most efficient wave function and calculation method two 24 factorial designs were considered and the results were discussed in this procedure. (C) 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part A 38: 269279, 2011