Refinement of molecular mechanics parameters for deformed benzene based on ab initio 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.