Main trends and the best candidate. Figure shows the energy barrier and the reaction energy for methane activation. It is clear that no Bell-Evans-Polyani trend, or its inverse, is observed. Interestingly, placing TMS at R 2 leads to elevated ∆E ‡ in excess of 120 kJ mol -1 and replacing this TMS with phenyl or perfluorophenyl markedly reduces the barrier. It is also worth noting that phenyl at R 2 makes the reaction more exothermic whilst perfluorophenyl has an opposite effect. For fixed R 2 , the reaction becomes increasingly exothermic as R 1 goes from TMS to Ph to C 6 F 5 . However, there is no clear trend for the ) reaction energy (∆E rxn ) and activation energy (∆E ‡ ) for the C -H bond cleavage. R 1 and R 2 groups are defined in Figure , whereas structure A, and B are shown in Figure . The red star labels the proxy to the imide proposed by Nikonov et al. activation barriers when varying R 1 .