Tuesday, September 27, 2011

What's in a name?

The IUPAC distinguishes "Lewis acidity" from "electrophilicity": the first concept relates to the equilibrium constant of the reaction of an electrophile (i.e. the termodynamics), whereas electrophilicity is related to the rate constant (i.e. the kinetics) of the reaction. However, the actual usage of the words in ordinary chemical parlance is somewhat more ambiguous, as the concepts are often used interchangeably.
A recent paper on this topic "Separating Electrophilicity and Lewis Acidity: The Synthesis, Characterization, and Electrochemistry of the Electron Deficient Tris(aryl)boranes B(C6F5)3–n(C6Cl5)n (n = 1–3)" caught my attention. However, this paper does not compare the changes in thermodynamics vs. kinetics ofthe title compounds upon increasing n. It rather compares their Lewis acidity with their ability to capture an electron (which the authors call electrophilicity). Quite a difference, don't you think?

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