SCALED QUANTUM-MECHANICAL (SQM) FORCE-FIELD AND VIBRATIONAL ASSIGNMENT FOR STYRENE

The geometry and complete harmonic force field for styrene were determ ined from ab initio Hartree-Fock calculations using the 4-21 gaussian basis set. Following the method of scaled quantum mechanical (SQM) for ce fields, systematic errors characteristic of this level of theory we re corrected empirically. The scale factors were taken over fixed from benzene and butadiene so that the final SQM force field represents pu re a priori results. Frequencies calculated from this force field repr oduce the experimental values with a mean deviation of 13.9 and maximu m deviations within 20 cm-1. The torsional potential around the C-C bo nd between the ring and the vinyl group was also investigated, also us ing larger basis sets. All calculations give a gauche form as the mini mum, but the potential is extremely shallowing thus justifying a vibra tional treatment on the basis of planar geometry. For comparison, test calculations on cis- and gauche-butadiene are also reported.