Torsion potentials and electronic structure of trifluoromethoxy- and trifluoromethylthiobenzene: an ab initio study

Abstract

Potential functions of internal rotation about the C sp 2 X bonds in molecules C 6H 5XCF 3 (X=O, S) were calculated at the second-order Møller–Plesset perturbation level of theory with 6-31G(d) basis set. The profile of the potential function and the rotation barrier (Δ E #=3.0 kJ/mol) found for C 6H 5OCF 3 suggest that, depending on experimental conditions, there can be either free rotation about the C sp 2 O bond or the conformational equilibrium is shifted to the side of the orthogonal form. The rotational barrier for C 6H 5SCF 3 is 14.7 kJ/mol and the molecule exists in the stable orthogonal conformation. The nature of hybridization, energy and population of lone electron pairs (LPs) on the oxygen and sulfur atoms were considered by using the Natural Bond Orbital (NBO) method. The energy of interactions of the LPs with antibonding π ∗-orbitals of the aromatic moiety were estimated for different conformations. The distribution of electron density in the molecules was discussed. The results were compared with analogous calculations on the molecules C 6H 5XCH 3.