To rationalize the observed trend of effective activation energies, we have tried to correlate these changes with descriptors, characterizing the coupling between the phenyl ring (Ph) and the benzonitrile oxide group -CNO. The descriptors used were the bond order of the Ph-CNO formally single bond and the net atomic charge of the phenyl group. Mayer bond orders were tested, whereas for the atomic charges, we used Mulliken, Löwdin, and Hirshfeld partitions. The results can be seen in Figure . Detailed information is available in the Excel file in the ESI.