TORSIONAL POTENTIAL FOR THE WEAK C(SP(2))-C(SP(2)) BOND IN BUTADIENE, BIPHENYL AND STYRENE

The transferability of the torsional potential of the C(sp(2))-C(sp(2)) weak double bond in the molecular mechanics method was investigated using a set of simple model molecules: biphenyl, styrene, alpha-methylstyrene, cis-beta-methylstyrene, 1,3-butadiene, isoprene, and 2,3-dimethylbutadiene. Individual torsional potentials for these molecules as well as different general potentials were derived. In the optimization of the torsional parameters, conformational energies from ab initio calculations at the Hartree-Fock level, and well-assigned torsional vibrational frequencies, were used.