DOI:10.1021/jp1003159

Ab Initio Study of Nonadditivity Effects: Spin-Spin Coupling Constants for Tetrafluoroethene in Ternary pi Complexes

C₂F₄ coupling constants have been evaluated at EOM-CCSD/(qzp,qz2p) in binary complexes with electron donors X (X = HLi, Cl⁻, CN⁻) and with the electron acceptor FH, and in ternary complexes FH:C₂F₄:X in which X and FH are located on opposite faces of the C₂F₄ π cloud. The electron donors X and the electron acceptor FH have opposite effects on ¹J(C−C), ¹J(C−F), ²J(C−F), and ³J(F−F) in binary complexes. Effects of X and FH on a particular coupling constant in a ternary complex are additive if the change in the coupling constant in this complex relative to C₂F₄ is within 1 Hz of the sum of the changes in the corresponding binary complexes. This is the case for ¹J(C−F). Both positive and negative nonadditivities are computed for the remaining coupling constants. Although the values of most coupling constants lie between the values for FH:C₂F₄ and C₂F₄:X, that is not the case for ²J(C−F), and the effect of FH is enhanced by the presence of X. Moreover, values of ³J(F−F) trans and cis for FH:C₂F₄:X when X is Cl⁻ or CN⁻ bonded through C are within 1 Hz of the values for the corresponding binary complex C₂F₄:X. Significant differences can be found between the relative contributions of the PSO, FC, and SD terms to total J and to the nonadditivities of J in ternary complexes FH:C₂F₄:X.