Dioxetane Radical Cations in Solution. An ESR and Cyclic Voltammetry Study

Article abstract of DOI:10.1021/ja00265a030

The radical cation formed upon electrochemical oxidation either of adamantylideneadamantane 1 in an O2-saturated solution or of the corresponding dioxetane 2 is shown by ESR spectroscopy to be 2⁺.This radical cation is relatively long-lived in CH2Cl2:CF3CO2H:(CF3CO)2O solvent mixtures at low temperatures.The resolved hyperfine splittings are 0.325 mT (4H) and 0.075 mT (6H).Using deuterated derivatives, the larger splitting has been assigned to two pairs of γ_eq-protons and the smaller one to the two remaining pairs of γ_eq-protons and one pair of β-protons, with each β-proton situated in a different adamantylidine moiety of 2⁺ (the notation β and γ_eq refers to the stucture of 1).These data are consistent with a C₂ conformation of 2⁺ which is twisted at the dioxetane ring and does not enantiomerize on the hyperfine time scale at -110 deg C.Dioxetane radical cations 11⁺ and 13⁺ generated from isopropylideneadamantane 10 and 3-pentylideneadamantane 12, respectively, have also been studied under similar conditions by ESR spectroscopy.Their hyperfine data give no evidence of twisting at the dioxetane rings and provide a further example for the sensitivity of the long-range splittings to orientation of bonds relative to the spin-bearing orbital.Cyclic voltammograms indicate that the E^o' value for 2 is 0.66 V anodic of 1 at -78 deg C, so that electron transfer from 1 to 2⁺ is exothermic by 15 kcal/mol.