Scales of Nucleophilicity and Electrophilicity: A System for Ordering Polar Organic and Organometallic Reactions

Contrary to widely held opinion, for many reactions in organic and organometallic chemistry it is possible to define nucleophilicity and electrophilicity parameters that are independent of the reaction partners. This phenomenon, discovered by Ritchie during the early 1970s for reactions of highly stabilized carbenium and diazonium ions with n‐nucleophiles, also occurs with reactions of carbenium ions with aliphatic and aromatic π‐electron systems and in hydride transfer reactions. With the aid of the scales of nucleophilicity and electrophilicity set out here, which extend over eighteen orders of magnitude, forecasts can be made about the feasibility and rate of a given CC bond formation, ionic reduction, or diazo coupling. Linkage with the reactivity scales of Ritchie and Sweigart/Kane‐Maguire enables a unified treatment of a large number of polar reactions. Is a particular reaction between an electrophile and a nucleophile feasible? This question often arises in synthesis design (symbolically represented on the right). Here electrophilicity and nucleophilicity scales are proposed that can give helpful answers. However, setting up an electrophilicity scale that is independent of the nucleophile contradicts the reactivity‐selectivity principle. This is recognized as a special case.