ESR. Spectra and Structures of Radical Anions in the Dibenzo[<i>a, e</i>]cyclooctene Series

Abstract

Abstract ESR. studies are reported for the radical anions of 5,6‐didehydro‐ and 5,6,11,12‐tetradehydro‐dibenzo[ a,e ]cyclooctene (III and IV, resp.), in addition to that of dibenzo[ a,e ]cyclooctene (II) itself, the spectrum of which has been reexamined. Comparison of the proton and 13 C coupling constants for II·⊖, III·⊖ and IV·⊖ indicates that the three radical anions do not differ greatly in their electronic and molecular structures. This statement implies that II·⊖ should also be substantially planar, i.e. , the tub‐shaped eight‐membered ring in II is expected to flatten on passing from the neutral molecule to its radical anion. Support for postulating such a change in geometry, analogous to that encountered with the parent cyclooctatetraene (I), is provided by INDO calculations.