Computational studies of fluorinated propenes: the fluorine "cis effect," barrier heights of the internal rotation of CX3 (X = H or F) group, and π-bond strengths

Abstract The (E)- and (Z)-geometrical isomers of fluorinated propenes (CWZ = CY—CX3, W, X, Y, and Z = H or F) are computationally investigated. Our calculations show that geometrical isomers with two fluorine atoms located at the cis positions of the C = C bond tend to undergo additional energy lowering compared to the trans isomers. Natural bond orbital analysis suggests that the origin of this lowering of energy is the same as that of the typical fluorine cis effects observed for 1,2-dihaloethenes. The barrier height magnitude of the internal rotation of the methyl or trifluoromethyl group is shown to be sensitive to the substitution patterns in the fluorinated propenes. The change in the rotational barrier heights is closely related to the differences in the magnitude of intramolecular repulsive non-bonded steric interactions. Furthermore, the π-bonds in fluorinated propenes are shown to be weaker for the derivatives possessing two fluorine atoms at both ends of the C = C bond. The OH radical reactions of the fluorinated propenes are initiated by the attack of the OH radicals on the π-bond. Nevertheless, no obvious correlation is found between the rate constants for the OH radical reactions and the π-bond strengths of the fluorinated propenes.