Radical cations of oxygen-containing organic compounds generated by gamma-irradiation of dilute freon solutions : an electron spin resonance study

The radical cations of several classes of oxygen-containing organic compounds have been generated by y-irradiation of dilute solutions in solid perhalocarbon (freon) matrices, and detected and characterized by the Electron Spin Resonance technique, including those of ether, acetal, aldehyde, ketone and epoxide compounds.

Acetal radical cations are found to be oxygen-centered radical species, and show very large hyperfine interactions (up to 160 G) to the hydrogens on the methylene bridge linking the two oxygens, in accord with the Whiffen effect. Replacenent of one methylene hydrogen with an alkyl group results in rearrangement to give the corresponding neutral alkyl radical at 77 K.

Aldehyde and ketone radical cations are found to be oxygen-centered σ radicals, aldehyde cations exibiting large coupling to the aldehydic hydrogen. Long-range hyperfine interactions to σ -hydrogens has been unequivocally proven to require a co-planar (W-plan) arrangement by isotopic substitution of an equatorial σ -hydrogen in 2-adamantanone.

Epoxide compounds are found to give a C...C ring-opened ²A₂ planar radical cation in several freon matrices (CCFCl₃ , CF₃CCl₃, and OCl₄). The C...C ring-opened planar structure of the oxirane radical cation has been conclusively proven by an ESR study of the doubly-labeled ¹³C oxirane radical cation. Localized forms of the C...C ring-opened cations of oxirane and oxirane derivatives are detected in the CFCl₂CF₂Cl matrix.