Ro-torsional energy correlation between the high barrier and free-internal-rotor limits: The case of the skew chain molecule HSOH

► Torsional motion in HSOH is described by the coordinate ρ. ► Scaling the torsional potential energy function changes the energy level structure. ► Free-rotor-limit (fscale=0) energy splittings depend strongly and cyclically on K. ► Free-rotor-limit splittings correlate to high-barrier (fscale⩾0.5) splittings. ► Cycle of splittings depends on the ratio of moments of inertia of rotor moieties.