The global electrophilicity index as a metric for Lewis acidity.

The global electrophilicity index, GEI, is used as a general, quantitative and base-independent metric of Lewis acidity. This parameter has been benchmarked against the established fluoride ion affinity, FIA, for a range of 22 neutral and cationic Lewis acids from across the p-block, including boranes, trityl derivatives, phosphonium cations and sulfoxonium cations. As a demonstration of utility, the GEI is used to catalogue a library of fluoroaryl boranes as it provides a rapid tool for the comparison of a series of Lewis acids featuring peripheral substituent variation.