Internal dynamics and optical rotations predicted for O_h- and O-symmetric cubanes

(Equation Presented) B3LYP/6-31G(d) calculations find that cubanes, persubstituted with NO₂ or BF₂ groups, are predicted to undergo near-barrierless, internal disrotations. However, as a consequence of the intrinsically higher energies of eclipsed conformations for threefold than for twofold rotors, the threshold mechanisms for octamethyk octakis(trifluoromethyl)-, octakis(trichloromethyl)-, octakis(tribromomethy|)-, octasilylcubane, and octakis(trichlorosilyl)cubane are calculated to be mono- or conrotation. The cubanes with the larger substituents are predicted to be O-symmetric, resolvable, and thus optically active.