In some cases, B2PLYP optimizations showed signs of instability, never reaching the force thresholds required for convergence. When the energies seemed sufficiently converged to make an assessment of ground state spin and geometry, the lowest energy structure along the optimization path was selected. These unconverged structures are indicated in the Table . Because frequency calculations could not be performed on geometries that were not fully converged, B2PLYP was omitted from the construction of LFESRs and volcano plots.