Transformations of radical cations of 1,3-dienes, 1,4-dienes, and cyclopentene as studied by ESR technique in irradiated frozen freon matrices and by spin trapping technique in liquid phase

Transformations of the radical cations of 1,3-pentadiene, 1,4-pentadiene, 2,3-dimethylbutadiene, and cyclopentene generated by X-rays at 77 K were studied in Freon-11 and Freon-113 matrices. The 1,3-pentadiene radical cations rearrange to yield cyclopentene radical cations in the CFCl3 matrix at 77 K. Rearrangement does not occur in the Freon-113 matrix; instead, addition of the radical cation to a double bond yielding terminal allyl radical takes place. The 1,1-pentadiene radical cations possess planar structure in the CFCl3 matrix. These radical cations converted to pentadienyl radicals in the Freon-113 matrix. The 2,3-dimethylbutadiene radical cations are transformed to terminal allyl radicals in the Freon-113 matrix. The cyclopentene radical cations convert to cyclic allyl radicals in Freon-113 at 110 K via deprotonation at the sites with maximum spin density. The ring cleavage resulting in formation of distonic radical cations also occurs but as a minor process. The proposed mechanism of radical formation agrees well with the data obtained in studies of liquid hydrocarbons irradiated with X-rays at 293 K in the presence of the spin trap 2,4,6-tri-tert-butynitrosobenzene.