ANION-MOLECULE APPROACHES NON-KEKULE MOLECULES - THE RADICAL-ANION OFCYCLOPENTADIENYLIDENETRIMETHYLENEMETHANE AND DERIVATIVES

Cyclopentadienylidenetrimethylenemethane radical anion 4, the one-elec tron reduction product of the corresponding diradical 3, was generated by a gas phase ion-molecule reaction of 6,6-dimethylfulvene (5) with O-.-. Characterization was carried out by isotopic labeling to confirm the distonic structure of the radical anion. The results suggest that negative ion photoelectron spectroscopic experiments can be used to r esolve a conflict between theories regarding the nature (singlet or tr iplet) of the ground state of 3. In reactivity studies, the radical an ion 4 is a better nucleophile than its corresponding anion 6, a result similar to that found for the tetramethyleneethane radical anion 1. T he basicity of the radical anion 4 has been bracketed at approximately 354 +/- 3 kcal/mol. This study contains the first evidence that a dis tonic radical anion can react as a radical as well as an anion, a resu lt that will lead to further gas phase examination of the radicals in the distonic ion series.