EFFECTS OF ELECTRON CORRELATION ON THE SERIES C2HNF6-N (N=0-6) - GEOMETRIES, TOTAL ENERGIES, AND C-C AND C-H BOND-DISSOCIATION ENERGIES

Geometries for the molecules in the series C2HnF6-n (n = 0-6) and for the radicals produced by homolytic cleavage of the C-C and C-H bonds have been optimized at the MP2/6-31G(d,p) level. Total energies have been calculated at the MP2/6-311G(d,p)//MP2/6-31G(d,p) level. A few calculations at the MP4/6-311G-(d,p)//MP2/6-31G(d,p) level have been included to show that higher order correlation effects do not change the observed trends. The preferred conformations of the substituted ethyl radicals indicate that the gauche effect operates in the radicals as well as in the parent molecules. The C-C and C-H bond dissociation energies are reported as D0(298 K). The C-H bond dissociation energies indicate that C-H bonds can be stabilized by an inductive effect from the beta-group and that the length of the bond does not correlate with the dissociation energy. Comparisons of results from HF and MP2 theory are made. Inclusion of electron correlation improves the geometrical parameters, in particular lengthening the C-F bonds, and the total energies. However, the use of correlated geometries as compared to the Hartree-Fock geometries has little effect on the bond dissociation energies.