On the usage of LDBS in the calculation of NMR indirect nuclear spin-spin coupling constant: vicinal F-F couplings

M. SANCHEZ, P. F. PROVASI, G. A. AUCAR AND S. P. A. SAUER

Advances in Quantum Chemistry

Elsevier

Lugar: San Diego, CA; Año: 2005; p. 161 - 184

Locally dense basis set were developed for correlated ab initio calculations of vicinal fluorine–fluorine indirect nuclear spin–spin couplings in several saturated and unsaturated fluorinatedhydrocarbons. We find that the choice of the basis set for each atom belonging to our studied modelcompounds depends on its location with respect to the coupled fluorine atoms and on the cis/transor synperiplanar/antiperiplanar conformation of the molecule. Carbon atoms in the bonding pathconnecting the coupled fluorine atoms have to be described with better basis sets than the carbonatoms outside this path. For the hydrogen atoms directly connected to the coupling pathway inmolecules with trans or antiperiplanar conformations and for all hydrogen atoms not directlyconnected to the coupling pathway one can employ a minimal basis set with only one s-function.Employing these type of LDBSs we can reduce the number of necessary basis functions by about30% without losing more than about 1 Hz in accuracy. The analysis of the four contributions tothe vicinal fluorine–fluorine coupling constants shows that the non-contact orbital paramagneticterm is the most important contribution followed by the also non-contact spin-dipolar term.The Fermi contact term is the largest contribution only in the synperiplanar conformations of1,2-difluoroethane and -propane.