Electron spin resonance study of the radical anions of substituted cyclooctatetraenes. The effects of Jahn-Teller distortions and vibronic mixing

The radical anions of methyl-, methoxy-, fluoro-, cyclopropyl-, and cyanocyclooctatetraene were generated by electrolytic reduction of the neutral compounds in liquid ammonia. The electron spin resonance spectrum of each radical anion is assigned, and a clean even--odd alternation of the spin densities is observed in each. This alternation can be correlated with the electronic properties of the substituent. For the radical anions of methyl-, methoxy-, and cyclopropylcyclooctatetraene, the temperature dependence of the coupling constants is reported. The results are accounted for in terms of vibronic mixing and Jahn--Teller distortions, and are discussed in relation to INDO calculations. 3 figures, 7 tables.