Nucleophilicity of reactive species through competition reactions: a demonstration with N-heterocyclic carbenes

<jats:p>This work reports the application of competition methodology to determine the nucleophilicity of reactive species. The efficacy of the method is demonstrated by the calculation of rate constants for the reaction of a series of electronically varied 1,2,4-triazol-5-ylidenes with a series of quinone methides; these data allowed the determination of the Mayr nucleophilicity parameters of these N-heterocyclic carbenes (NHCs). Along with generating extremely accurate nucleophilicity data, these experiments are general and require no specialist equipment, making the determination of nucleophilicity of reactive species more widely accessible.</jats:p>