Home – Home – Jornals – Journal of Structural Chemistry 2011 number 2

A quantum chemical study of the internal rotation of CX₃ (X = H, F, CH₃) radical substituents in scandium and calcium β-diketonate complexes is performed. Calculations are carried out using the GAUSSIAN-03 program at the HF and DFT/B3LYP levels with relativistic effective core pseudo-potentials and valence double zeta basis sets. Analytical expressions V(ϕ) are obtained that describe the potential energy variation during the rotation of СХ₃ groups. The rotation of CH₃ and CF₃ groups is shown to be described by a simple potential of the form V = V₀/2 + V₃cos(3ϕ), while for the description of the rotation of tert-butyl groups it is required to use a more complex function V = V₀/2 + V₃cos(3ϕ) + V₆cos(6ϕ). Based on the obtained expressions for V(ϕ), the effective torsion angles ϕ_ef of the rotation of СХ₃ groups are calculated for different temperatures. It is shown that ϕ_ef obtained based on the quantum chemical calculations are close to the values obtained in electron diffraction experiments.