EFFECTS OF ELECTRON DONATION INTO C-F SIGMA-ASTERISK ORBITALS - EXPLANATIONS, PREDICTIONS AND EXPERIMENTAL TESTS

The ability of C-F sigma orbitals to act as electron accepters is sho wn to be capable of explaining and predicting a wide variety of appare ntly unrelated phenomena. Among these are (i) pyramidalization of fluo rinated radical centers, (ii) the much weaker pi-bond in tetrafluoroet hylene (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 replac ing 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 substit ution of fluorines for the pair of hydrogens at C-2 of cyclopentane-1, 3-diyl.