An Experimental Radical Electrophilicity Index.

We present an experimental electrophilicity index (ϻ) for the classification of radicals. The ϻ-scale is based on the equilibrium constant determined for the reversible addition of a radical R. to an aromatic radicophile (HisNH2 ). This experimental approach is in excellent agreement with the computed global electrophilicity index ω and serves to validate the latter.