While prior studies demonstrate successful fluorination of some substrates, typically without heteroatoms , pharmacologicallyactive drugs often involve the presence of fluorine in heterocycle rings, steroids (and their derivatives), etc., including N and/or O heteroatoms . In this study, we first aim to understand the ground spin state of the Mn-porphyrin intermediates as predicted by hybrid density functional theory (DFT) and its sensitivity to the functional. We then compute reaction energies along the catalytic cycle for substrates used in prior experimental studies to estimate a possible role of thermodynamic factors in the control of reactivity and regioselectivity of Mn-porphyrin-catalyzed fluorination. Lastly, we obtain potential energy curves along the reaction coordinate for C-H fluorination, for the simplest cases of cyclohexane and piperidine (representatives of active and nonactive substrates, respectively, for Mn-porphyrin-catalyzed fluorination) to understand why fluorination of drug-like compounds with heteroatoms does not occur as simply as fluorination of hydrocarbons.