The anion radical of cyclooctatetraene (COT) must undergo a Jahn-Teller distortion from its ideal D-8h 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 D-4h alternating bond angle conformations (a b(1g) distortion). The rapid (k = 3 x 10(7) 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)(2)COT-.], on the other hand, has a ground state with alternating bond lengths. Since this bz, 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 b(1g) and b(2g) distorted COT-. ring systems of less than 1 kcal/mol. In support of this, the EPR data are best simulated in terms of the presence of both Jahn-Teller distorted forms of the anion radical.