Observation of Both Jahn−Teller Distorted Forms (b1g and b2g) of the Cyclooctatetraene Anion Radical in a 1,2-Disubstituted System

Abstract

The anion radical of cyclooctatetraene (COT) must undergo a Jahn−Teller distortion from its ideal D8h symmetry. Both B3LYP/6-31+G* calculations and EPR observation have shown that the COT moiety in the anion radical of 1,2-dicarbo-tert-butoxycyclooctatetraene exists in a pair of degenerate D4h alternating bond angle conformations (a b1g distortion). The rapid (k = 3 × 107 s-1) interconversion between the two identical conformations leads to specifically predicted line width alternation effects in the EPR spectrum. The COT ring system in the 1,2-dicarbomethoxycyclooctatetraene anion radical [(CH3OOC)2COT-•], on the other hand, has a ground state with alternating bond lengths. Since this b2g distorted (COT-•) system has a plane of symmetry that can be drawn through the molecule and between the two substituents, no line width alternation effects can take place. However, in this system, the B3LYP/6-31+G* calculations predict an energy difference between the b1g and b2g distorted COT-• ring systems of less tha...