The non-redox diazonium salt dC12 was mixed with a stoichiometric amount of bare TEMPO, and the system's evolution was subsequently monitored by 1 H NMR, as shown in Figure -bottom. The addition of TEMPO to the NMR tube containing dC12 caused a noticeable shift in the aromatic proton peaks (a and b) to lower chemical shifts (a' and b'). This shift suggests a transformation of the diazonium group into a less electron-withdrawing group, likely due to a reduction reaction that generates aryl radicals. This hypothesis points to a redox reaction where the diazonium salts are reduced, and TEMPO species are oxidized to form oxoammonium cations. However, the possibility of radical coupling-either between aryl radicals themselves or between aryl radicals and TEMPOcannot be excluded, as such coupling reactions could also explain the observed decrease in the chemical shifts of the aromatic protons.