ABINITIO MOLECULAR-ORBITAL CALCULATIONS OF THE INTERNAL-ROTATION OF STYRENE WITH ELECTRON CORRELATION USING THE POLARIZED 6-31G-STAR BASIS SET

The energies of styrene at various torsional angles have been calculated with full geometry optimization using the polarized 6-31G* basis set. The torsional angle of the conformer of minimum energy obtained by HF/6-31G* calculations is 15.02°. The internal rotational barrier heights at 0° and at 90° obtained with HF/6-31G* calculations are 0.04 and 2.88 kcal/mol, respectively. A Møller-Plesset fourth-order perturbation treatment of the HF/6-31G* optimized geometries (MP4-(SDQ)/6-31G//HF/6-31G*) gives barrier heights of 0.10 and 2.48 kcal/mol, respectively. The calculated barrier height at 90° is lower than the barrier height of 3.13 kcal/mol, recently obtained by HF/6-31G calculation. The effect of the polarized basis set and of the electron correlation on the calculation of the rotation about the C1-Cα bond of styrene is discussed with reference to the calculations on 1,3-butadiene. © 1990 American Chemical Society.