A molecular mechanics (MM3) study of fluorinated hydrocarbons

A molecular mechanics study of small saturated hydrocarbons (up to C-6), substituted by up to six fluorines was carried out with the MM3 force field. Perfluorobutane and Teflon were also studied. A parameter set was developed for use in the calculation of bond lengths, bond angles, torsion angles, conformational energies, barriers to rotation, dipole moments, moments of inertia and vibrational frequencies for these compounds. The results are in good agreement with experiment when only one or two fluorines are present, but some rather large discrepancies were noted when the F/H ratio becomes high. These can be taken into account only by using a force field more complicated than MM3. Some of the requirements of such a force field are delineated. Some pertinent ab initio results are also reported in this article.