Computational multireference simulations supported these experiments. Using the Complete Active Space Self-Consistent Field (CASSCF) approach, we found that the T1 state was stabilized during N-O bond rupture induced by end-to-end stretching of MKO and TKO (Figure ). This observation was further underpinned using the Spin-Flip TD-DFT approach to calculate the number of unpaired electrons, which transitioned from zero to two upon bond rupture (Figure ). This finding plausibly explained the thermal stability of the N-O bond in the ketoxime derivatives, since (i) direct access to the reactive T1 state is spin forbidden and (ii) the Ei mechanism cannot proceed as it involves the transfer of a proton, which is replaced with R = Me or tBu in the ketoximes.