The Willgerodt reaction[1], discovered in 1887 and shown below, represents a transformation with a once famously obscure mechanism. A major step in the elucidation of that mechanism came[2] using the then new technique of <sup> 14 </sup> C radio-labelling, shortly after the atom bomb projects during WWII made <sup> 14 </sup> CO <sub> 2 </sub> readily available to researchers.