Electron spin resonance study of the interaction between radical ion pairs and macrocyclic polyethers

The alkali metal ion pairs of 2,2?-bithiazolyl, bisthiazol-2-yl ketyl, bis-2-thienyl ketyl, and of two symmetrical dithienothienyl ketyls have been studied by e.s.r. in ethereal solutions in the presence of dibenzo-18-crown-6 ether. The conformational stability of the latter three ketyls is much affected by the complexation of the ion pair by the cyclic ether. The sodium complexes show also a large enhancement of the energy barrier to the rotation of the aromatic groups. These results have been interpreted by postulating a sandwich structure for the crown complexes of the sodium ketyls.