Dative and Electron-Sharing Bonding in C₂F₄

The reaction pathway for the rupture of the carbon–carbon double bond of C₂F₄ has been calculated with ab initio methods at the CASSCF(8,8)+NEVPT2/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ levels and with density functional theory using M06-L and M06-2X functionals in conjunction with aug-cc-pVTZ basis sets. The calculations suggest that the bond dissociation pathway proceeds by a nonlinear reaction course without an activation barrier yielding the CF₂ fragments in the (¹A₁) ground state. A bonding analysis indicates that there is a continuous change in the electronic structure of the CF₂ fragments during the elongation of the C–C distance from a (³B₁) excited state at the equilibrium geometry of C₂F₄ to the (¹A₁) ground state. EDA-NOCV calculations suggest that the carbon–carbon interactions in C₂F₄ at equilibrium distance and longer C–C values up to ≈1.60 Å are best described in terms of electron-sharing bonding between the CF₂ fragments in the (³B₁) excited state. At longer distances, the situation changes toward dative bonding between CF₂ fragments in the (¹A₁) ground state.