Kinetics of the Solvolyses of Benzhydryl Derivatives: Basis for the Construction of a Comprehensive Nucleofugality Scale

A series of 21 benzhydrylium ions (diarylmethylium ions) are proposed as reference electrofuges for the development of a general nucleofugality scale, where nucleofugality refers to a combination of leaving group and solvent. A total of 167 solvolysis rate constants of benzhydrylium tosylates, bromides, chlorides, trifluoroacetates, 3,5‐dinitrobenzoates, and 4‐nitrobenzoates, two‐thirds of which have been determined during this work, were subjected to a least‐squares fit according to the correlation equation log  k 25 °C = s f ( N f + E f ), where s f and N f are nucleofuge‐specific parameters and E f is an electrofuge‐specific parameter. Although nucleofuges and electrofuges characterized in this way cover more than 12 orders of magnitude, a single set of the parameters, namely s f , N f , and E f , is sufficient to calculate the solvolysis rate constants at 25 °C with an accuracy of ±16 %. Because s f ≈1 for all nucleofuges, that is, leaving group/solvent combinations, studied so far, qualitative discussions of nucleofugality can be based on N f .