The reaction is nevertheless not a perfect runaway chain reaction, as it does require continued irradiation to reach completion. In addition to cyano-aryl radical anion quenching, there is another deactivation pathway, whereby the ester radical anion reduces a DABCO cation to reform the starting EDA complex (Fig. ). This process is thermodynamically favourable (-41.3 kcal mol -1 ) but less likely to occur, as it involves two short-lived radical species that are present in only small concentrations.