The STO 3G MO structure and internal rotational potential of benzophenone

Abstract
Extensive geometry-optimized STO 3G MO computations yield C2 symmetry and 32° for the twist angles of the phenyl groups in benzophenone. For the planar molecule the internal rotational barrier is 33.7 kJ/mol and is 24.6 kJ/mol for a twist angle of 90°. The expectation value of the twist angle is therefore very near 32° at 298 K; implying that, in the crystal, packing forces cause only a minor perturbation of the conformation, the angle being 30° in the solid. An energy profile for non-C2 symmetry is also computed.