Thermodynamic Evaluation of Aromatic CH/π Interactions and Rotational Entropy in a Molecular Rotor

A molecular rotor
built with a stator formed by two rigid 9β-mestranol
units having a 90° bent angle linked to a central phenylene rotator
has an ideal structure to examine aromatic CH/π interactions.
Energies and populations of the multiple solution conformations from
quantum-mechanical calculations and molecular dynamics simulations
were combined with variable-temperature (VT) 1H NMR data
to establish the enthalpy of this interaction and the entropy associated
with rotation about a single bond. Rotational dynamics in the solid
state were determined via VT cross-polarization magic-angle spinning 13C NMR spectroscopy.