Conformational energy differences were assessed as follows. Compound conformers were energyminimized using QM. For a compound with at least three conformers, we identified the conformer with the lowest QM energy , and computed the energies of its other conformers relative to it: , -, . We then computed the force field energies of the same conformers, , , and, for each compound, computed the RMSE of , -, from the corresponding QM energies. Note that conformation is based on the QM energies and used again for the FF energies.