Theoretical Study on the Molecular Geometries of Substituted Fluoroforms

The F…F non-bonded distances are strikingly constant in a large series of trifluoromethyl derivatives. Semiempirical NDDO calculations have been performed for five representative molecules. From the energy partitioning it appears that the bonding interactions (resonance energy terms) are dominating in determining the molecular geometry. The constancy of the non-bonded distances may occur as the changes in the bond lengths and bond angles are compensated. A good description of the total energy, however, necessitates the inclusion of the two-center electrostatic terms of all atom pairs.