R. Hargitai et al., SCALED QUANTUM-MECHANICAL (SQM) FORCE-FIELD AND VIBRATIONAL ASSIGNMENT FOR STYRENE, Journal of molecular structure. Theochem, 112(2-3), 1994, pp. 293-311
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.