Pérez-Estrada, S.; Rodríguez-Molina, B.; Xiao, L.; Santillán, R.; Jiménez-Osés, G.; Houk, K. N.; Garcia-Garibay, M. A. ?Thermodynamic Evaluation of CH/? Interactions and Rotational Entropy in a Molecular Rotor? J. Am. Chem. Soc. 2015, 137, 2175-2178, DOI: 10.1021/ja512053t.
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.