Radical cations of cyclopropane systems

RADICAL CATIONS OF CYCLOPROPANE SYSTEMS CONJUGATION AND HOMOCONJUGATION WITH ALKENE FUNCTIONS... 

The Radical Cations of the System Quadricyclane — Norbornadiene No discussion about cyclopropane radical cations would be complete without reference to the quadricyclane radical cation (Q-+) and its valence isomer, the... 

ELECTRON TRANSFER PHOTOCHEMISTRY OF CYCLOPROPANE SYSTEMS RADICAL CATION REACTIVITIES... 

In general, radical cations of alkenes or cyclopropanes produce nonconjugated radicals, while those of dienes give rise to allyl radicals, and those of vinylcyclopropane or vinylcyclobutane systems generate either allylic or nonconjugated radicals with an additional element of unsaturation. In contrast to the most thoroughly characterized nucleophilic substitution of appropriate neutral molecules. 

However, electron transfer-induced photoreactions in the presence of nucleophiles have attracted by far the greatest attention a rich variety of cyclopropane systems have been subjected to these reaction conditions. We will consider several factors that may affect the structure of the radical cations as well as the stereo- and regiochemistry of their nucleophilic capture. Factors to be considCTcd include (1) the spin and charge density distribution in the cyclopropane radical cation (the educt) (2) the spin density distribution in the free-radical product (3) the extent of... 

Radical cations of the same general structure type as those derived from cis- and tratw-diphenylcyclopropane have been established for numerous cyclopropane derivatives, including the parent, 1,2-di-, 1,1,2-tri- and 1,1,2,2-tetramethylcyclo-propane (Table 3). Two of these systems provide a direct comparison between the results of CIDNP and ESR experiments. In both cases, the ESR spectra observed by Williams and coworkers following pulse radiolysis in frozen solutions [293, 296, 297] show splitting patterns supporting the presence of spin density on two carbon centers, thus confirming the structure type (102) assigned on the basis of CIDNP results. 

In analogy to substituent effects discussed for the cyclopropane system, we point to the possibility that 1,1-disubstitution may stabilize cyclobutane radical cations of type D. To our knowledge, such a structure has not materialized to date. 

Table 4. H Hyperfine coupling patterns constants for radical cations of selected cyclopropane systems.

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