Tetramethyleneethane radical cations

Upon y-irradiation of 1 in a CF3CCI3 matrix at 77 K [78], a radical cation was formed, the ESR spectrum of which consisted of nine broad hyperfine components spaced by ca. 0.75 mT (g = 2.0029 0.002), and the corresponding proton END OR spectrum exhibited two essentially isotropic signals at 25.83 and 24.58 MHz. The detailed analysis of the ESR and END OR spectra disclosed that the initially formed radical cation 1+ had transformed into the tetramethyleneethane radical cation 94+ (Scheme 17). In CFCI3 and CF2CICFCI2 matrices 1+ persists up to 100 K [79]. On going from 1 to l+, the set of eight equivalent protons splits... 

Scheme 17. Tetramethyleneethane radical cation 94+ formed from bicyclopropylidene (1) and bonding linear combinations of the Walsh orbitals for 1 [78-80]...

Fig. 30. ESR spectrum of tetramethyleneethane radical cation in a CF3CC13 matrix at 140 K with H ENDOR signals observed above the free proton frequency as an inset a stick diagram of the ESR spectrum is shown on the bottom (Reprinted by permission)...

Although electron-transfer-promoted reactions of 89 are unknown, cation radical 95 has been generated by y-irradiation and its matrix-dependent reactivity was recently reported by Gerson and his co-workers. In a CF3CCI3 matrix at 77 K, 95 rearranges rapidly to the bisected tetramethyleneethane cation radical 96. However, deprotonation occurs at 120 K in a CFjClCFClj matrix to form 97 (Scheme 26). It is reasonable to assume that cation radical 96 is formed by the cyclopropyl-allyl rearrangement of 94 itself generated from 95. ... 

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