Scaled quantum mechanical (SQM) force field and vibrational assignment for styrene

Abstract

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