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

A molecular rotor built with a stator formed by two rigid 9?-mestranol units having a 90 bent angle linked to a central phenylene rotator has an ideal structure to examine aromatic CH/? 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.