Effects of electron donation into C–F σ* orbitals: explanations, predictions and experimental tests

Abstract

The ability of C–F σ* orbitals to act as electron acceptors is shown to be capable of explaining and predicting a wide variety of apparently unrelated phenomena. Among these are (i) pyramidalization of fluorinated radical centers, (ii) the much weaker π-bond in tetrafluoroethylene (TFE) than in ethylene, (iii) the stepwise reaction of TFE with butadiene to form 2,2,3,3-tetrafluoro-1-vinylcyclobutane, rather than the Diels–Alder adduct, (iv) the thermodynamic favorability of replacing C–H with C–C bonds at fluorinated carbons, (v) the preference for disrotatory ring opening and closure of 1,1-difluorocyclopropanes, and (vi) the change from a triplet to a singlet ground state upon substitution of fluorines for the pair of hydrogens at C-2 of cyclopentane-1,3-diyl.