In this study, firstly, we looked at the ground spin states of various intermediates observed along the C-H fluorination catalytic cycle. We observed that the energies of various spin states are close to each other (differences comparable to kT), and the identification of the ground state is highly sensitive to the used density functional. We hypothesize that the Mn complex may enter the rate-limiting step of the catalytic cycle most likely in an intermediate-spin quartet state, though the low-spin doublet state may also be reachable in terms of energy. More accurate and much more expensive wavefunction theory methods might help further clarify the ground state of these intermediates with more certainty. On the other hand, relatively small differences in the predicted energies of various spin states may imply that the ground states are sensitive to experimental conditions under which fluorination is performed, and transitions between different spin states might be a real phenomenon rather than a computational artifact. If so, this observation may suggest an additional potential direction to control the regioselectivity and yield of the reaction via factors that affect the spin states, e.g., by modifications of the peripheral parts of the porphyrin ligand, which would fine tune the strength of the ligand field. Secondly, we looked at the reaction energies for various substrates and found that the reaction energies of active and inactive substrates are mostly comparable, indicating that thermodynamic factors may not play the central role in determining whether a certain substrate molecule can undergo catalyzed fluorination. Thirdly, based on these results, we hypothesized that the determining factor might be the reaction barrier and the properties of the corresponding transition state. For a preliminary estimation of plausibility of such an explanation, we carried out 1D potential energy scans for reaction pathways for piperdine and cyclohexane, and found that the energy barrier for fluorination of piperidine is almost six times higher than that of cyclohexane, and significantly exceeds the energies reachable by thermal fluctuations, in agreement with the assignment of these two substrates to non-reactive and reactive classes, respectively. We speculate that the high energy barrier in case of piperidine could be due to the formation of a more stable substrate system due to the lone pair of nitrogen stabilizing the carbon radical or the formation of a more stable complex with fluorine. This interpretation, however, requires further computational investigation. While we modeled Mn-porphyrin complexes in this work, some of our results may be relevant for understanding other fluorination reactions, for example, benzylic C-H fluorination using Mn-salen catalysts.