Polarographic reduction of some Schiff bases in dimethylformamide

The half-wave potentials of a series of Schiff bases of the type [Formula: see text], where Ar and Ar′ are unsubstituted aryl groups, have been measured in dimethylformamide. The effect of structural variations of the aryl groups Ar and Ar′ on these potentials have been calculated by the linear combination of molecular orbitals (l.c.m.o.) variant of the Hückel molecular orbital (H.m.o.) theory without specific consideration of the nitrogen heteroatom present in these compounds. It is demonstrated that the equation which relates E 1/2 for the first electron transfer to theoretical quantities calculated by the l.c.m.o. theory can be applied to the data in several ways, one of which shows an interesting analogy with the Hammett σ−ρ treatment of linear free energy relationships.