Alkoxycyclooctatetraene Anion Radicals: An Unusual Spin Density Perturbation Due to 1,3-Carbon/Carbon Interactions

A series of new alkoxycyclooctatetraene ethers was synthesized and their anion radicals generated in hexamethylphosphoramide. The EPR measured spin densities can be explained in terms of the odd electron occupying MOs, Ψ 4 ‘ = [1/2√( n 2 + 1)]( n ψ 1 + ψ 2 − n ψ 3 − ψ 4 + n ψ 5 + ψ 6 − n ψ 7 − ψ 8 ) and Ψ 5 ‘ = [1/2√( n 2 + 1)]( n ψ 1 − ψ 2 − n ψ 3 + ψ 4 + n ψ 5 − ψ 6 − n ψ 7 + ψ 8 ), where n increases with the electron-releasing nature of the alkoxy group. The anion radicals of n -propoxycyclooctatetraene and ibuprofoxycyclooctatetraene exhibit a small (ca. 0.35 G) splitting for the γ proton on the sp 3 hybridized carbon. Further, the EPR pattern for the tert -butoxycyclooctatetraene anion radical is consistent with a relatively smaller value for n (in Ψ 4 ‘ and Ψ 5 ‘). These observations are consistent with a rather unusual homohyperconjugative interaction involving overlap of the σ-bond to the γ-hydrogen and the π-system of the conjugated COT ring.