Ionization Energies of Methyl-substituted[2.2]Paracyclophanes

The photoelectron (PE.) spectra of thirteen methyl-substituted 2.2]paracyclophanes have been recorded and analyzed, to assess the influence of methyl-substitution on their ionization energies. It is shown that this influence is qualitatively and quantitatively the same as for benzenes and other π-systems. Comparison with the previous results obtained for the 2_r]cyclophanes (r=2 to 6) strongly suggests that the hyperconjugative model for alkyl-group/π-system interactions is more appropriate than the inductive one.