Polarization effect in radical cations and H-complexes

The effect of substituents X on the ionization potentials IP (process DX + hν ? D^+·X + e) and shifts in vibration frequencies Δν of ν(OH) in the IR spectra of phenol complexes PhO-H + DX ? PhO^δ?-H…D^δ+X for nine series of DX molecules were studied. On compiling with three conditions (a constant donor center D; the electron density donation only from D and not from X; a constant sampling size within each series) it was possible to compare the polarization effect in D^+·X and D^δ+X. In the radical cations D^+·X the polarization effect is on the average 2.2 times larger than in the systems D^δ+X. The systems D^+·X and D^δ+X are virtually indistinguishable with respect to the external delocalization of the positive charge.