Grubbs 3 and Matson also found that monosubstituted exo-NBs polymerize faster than disubstituted variants; Matson attributed this difference either to the possibility that monosubstituted monomers can form regioisomers where their substituents point away from the ruthenium center (a steric effect), or to electronic effects (HOMO level and HOMO/LUMO gap). While the chelating ability of NB monomer substituents has also been shown to significantly affect the activation parameters of polymerization and may slow the polymerization rate by ground-state stabilization in certain cases, the chelating ability of exo-NB monomers seems to have little correlation with their propagation rates. We note that NB-CO2Me has a ~4-fold larger kp than TCN-(CO2Me)2 despite having nearly the same calculated HOMO energy (0.6 kcal difference), and that TCND-(CO2Me)2 and TCND-CO2Me both have higher-lying HOMOs (by ~4 and ~6 kcal/mol, respectively) than NB-CO2Me but significantly lower kp values. Overall, while HOMO energy is a useful tool for predicting ROMP reactivity for exo-NB-like scaffolds, other effects, such as steric effects near the propagation site, may impact the rate as well.