(left) Calculated potential energy profiles for reactions of singlet-state [MnV(O)(TBP8Cz)(X)] (X = none (1), F (1-F), CN (1-CN)) with DHA; TS = transition state; Int = intermediate; Prod = product). (right) Transition state structures for the initial HAT step, with selected bond distances in angstroms, bond angles in degrees, and imaginary frequencies in wavenumbers. (bottom) Mechanism of HAT with DHA as the substrate. Adapted with permission from ref 19. Copyright 2010 John Wiley & Sons.