Balls and sticks models representing the stationary points and the two torsional angles for systems S1, S2, and S3. It also indicates the two torsional angles studied in each case. For S3 the hindered rotation ϕ1 is about the C, O atoms.
Colour contour plot of the energy landscape (in cm−1) resulting from the rotation about the two torsional angles. The solid-red and dashed-green lines when displayed, indicate the one-dimensional torsional potentials.
Plot of the ratio Q 2D–NS/Q STES at several temperatures. The ratios for systems S1, S2, and S3 are represented by filled squares, circles, and filled circles, respectively.
Plot of the ratio F q/F MC–PG at several temperatures. Symbols as for Fig. 3 .
Parameters (in cm−1) for the one-dimensional terms of Eq. (22) for the three systems.
Coupling parameters (in cm−1) of Eq. (22) for the three systems.
Partition functions for the three systems calculated at several temperatures. Q cl, tor, Q STES, and Q 2D–NS are given by Eq. (30) , Eq. (20) , and Eq. (28) , respectively. Q NS–V is calculated the same way as Q 2D–NS, but considering that the reduced moments of inertia are constant and calculated at the equilibrium geometries of the the absolute minima.
Some parameters of interest for the two internal rotations of the three systems. The minima S3-M1 and S3-M2 have enantiomers. The frequencies ω i, 1 and ω i, 2 correspond to normal-mode torsional frequencies, whereas , , and and are the frequencies calculated by Eqs. (35) and (36) , respectively. The zero-point energies (ZPE) calculated by the STES and 2D-NS methods are also indicated. All the frequencies, ZPEs, and the energy difference between conformers U i are given in cm−1. The reduced moments of inertia are given in amu Å2.
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