A theoretical study of the molecular structure and torsional potential of styrene

State-of-the-art ab initio methodologies have been used to perform calculations on the torsion along the vinyl-phenyl groups in styrene. The methods employed range from the Hartree-Fock and Möller-Plesset perturbation theories and coupled-cluster theory up to density functional (DF) ones. The effect of the basis set has also been considered by using several extrapolation formulae to the complete basis set limit. The torsional profile is analysed in terms of the π-conjugation and steric repulsions. The calculations indicate the existence of a global twisted minimum with a slightly lower energy than the planar structure. However, the exchange-correlation functionals used in the DF calculations are unable to predict this twisted minimum.