The Fluorophosphoranyl Series: Theoretical Insights into Relative Stabilities and Localization of Spin

The nine isomeric local minima within the complete fluorophosphoranyl series (H_nPF_4-n^* n = 0-4) have been investigated at the UHF/6-31G* and higher levels. Quantitative analysis of fluorine apicophilicity and hyperconjugative effects within the trigonal-bipyramidal series is presented. The ability of atomic orbitals on axially disposed fluorine atoms to participate in either a hyperconjugative donor or acceptor role is quite limited in comparison to analogous opportunities for equatorially disposed fluorine atoms. Decomposition of metathesis energy changes into apicophilic and hyperconjugative components permits rational evaluation of the corresponding equilibria. Localization of spin density is accomplished efficiently by using the calculated MP2/6-311G electron density. Fermi contact integrals derived therefrom allow for highly accurate prediction of isotropic hyperfine coupling constants after application of a small scaling factor. Techniques alternatively using s-orbital spin density for such predictions are far less satisfactory.