REFINEMENT OF MOLECULAR MECHANICS PARAMETERS FOR DEFORMED BENZENE BASED ON ABINITIO MOLECULAR-ORBITAL CALCULATIONS

The geometries and energies of deformed benzenes have been calculated by molecular mechanics with implementation of newly refined in-plane angle-bending-force constants and torsion parameters including those of the Car-Car bond, based on the deformation energies of benzene, toluene, and o-xylene obtained by MP4(SDQ)/6-31G* level ab initio molecular orbital calculations. The calculated geometries of cyclophanes and tetra-t-butylbenzene and the internal rotational barrier height of 2-isopropyl-1,3,5-trimethyl benzene agree well with the experimental values.