The Anion Radical of [18]Annulene

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2002-01, Vol.106 (3), p.478-481
• Main Authors: Kurth, Todd L, Brown, Eric C, Hattan, Chris M, Reiter, Richard C, Stevenson, Cheryl D
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp013524+

The anion radicals of [18]annulene and of [6]annulene undergo Jahn−Teller distortions from the D 6 h conformations of their respective neutral molecules. The conformation of lowest energy for the anion radical of benzene has a C2 v symmetry, and that for the anion radical of [18]annulene is D 2 h . The very rapid pseudo-rotation of the benzene C2 v system causes the six protons of the benzene anion radical to appear as if they were equivalent in the EPR experiment. Fast pseudo-rotation rendering the uniform distribution of spin density in the [18]annulene anion radical system is prevented by the nonplanarity of the radical. Hence, the EPR spectrum of the [18]annulene anion radical must be interpreted in terms of a static (on the EPR time scale) D 2 h conformation, which pseudo-rotates over a C 2 h transition state. B3LYP calculations support these conclusions.