Use of DFT-based reactivity descriptors for rationalizing radical addition reactions: applicability and difficulties.

The use of density functional theory-based reactivity descriptors, including global (hardness, electronegativity) and local (Fukui function, local softness) indices in rationalizing the reactivity and regioselectivity of radical addition reactions has been critically analyzed. We demonstrate that there is a severe inherent deficiency in the current way of defining the Fukui functions and local softness for radical attack parameters (f(0) and s(0)), and propose a (preliminary) alternative.