AB-INITIO SCF AND MP2 CALCULATIONS OF THE STRUCTURES AND RELATIVE STABILITIES OF THE ISOMERIC HYDROCARBONS C7H8

The molecular structures and relative stabilities of some selected hyd rocarbon isomers of the C7H8 species are reported at the HF/6-31G and MP2/6-31G levels of theory. Except for the strained bicyclic species, the relative energies obtained by ab initio calculations are found to be qualitatively in agreement with those of previous semiempirical MO and molecular mechanics studies. The calculated C-C and C = C bond len gths are, however, considerably different in some cases from the semie mpirical MO values.