EFFECT OF TEMPERATURE COUNTER-ION AND SOLVENT ON ABSORPTION SPECTRUM OF 4,5-METHYLENEPHENANTHRENE ANION

The absorption spectrum of the 4,5-methylenephenanthrene anion has been studied. In tetrahydrofuran solution and with sodium as the counter-ion the spectrum changes markedly with temperature. It appears that this change is best interpreted in terms of two different types of ion pair, i.e., contact and solvent-separated. The fraction of solvent-separated ion pairs, in a given solvent, decreases in the order Li > Na > K > Cs. The effect of solvent on the fraction of solvent-separated ion pairs, with the same counter-ion, is in the order 1,2-dimethoxyethane > tetrahydrofuran > 2- methyltetrahydrofuran > tetrahydropyran. ΔH° and ΔS° have been determined for each system studied and vary markedly with counter-ion.