Across almost all the substrates, rebound energies are also comparable, as well as release energies (Figure , Table ). Closer examination of rebound energies for cyclohexane and piperidine, which is obtained by replacing a carbon atom of cyclohexane with a nitrogen heteroatom, reveals that rebound energy is slightly more favorable for cyclohexane compared to piperidine (Figure , Table ). A similar comparison of release energies shows that release of fluorinated cyclohexane is slightly more favorable than fluorinated piperidine (Figure , Table ). Therefore, the reaction energies are comparable across different substrates, both capable and incapable of Mn-porphyrin-catalyzed fluorination, and cannot explain this difference in the reactivity. Table . Various reaction energies, namely, hydrogen atom transfer (HAT) energy (column 2), radical rebound energy (column 3), and product release energy (column 4) in kcal/mol for substrates studied in prior experimental work and piperidine. 'a' and 'b' correspond to diastereomers of the corresponding substrate. HAT energy is not available for piperidine.