In contrast to the previous study by Bally and Platz et al., 1, 2 we found that over the course of several hours the bands of 1 gradually disappeared (in the dark) while those of 4 slowly emerged (Fig. ). The observed reactivity of 1 under these experimental conditions with a half-life of 6 h can only be explained by QMT, in line with the prediction by Kozuch and our computational data (vide infra). Carbene 1, generated from irradiation of 5 at 365 nm, exhibits a UV/Vis spectrum with an absorption maximum at around 610 nm (Fig. ). After 18 h in the dark, this UV/Vis signal disappears completely, confirming the QMT reactivity observed also in the IR spectra. Only 4 was obtained, rendering 1 unsuitable for the investigation of ICS. Consequently, our attention shifted to 2.