Radicals 650 norbornyl cation

The initial studies centered on the 1-norbomyl halides 8. On irradiation in CH3OH, they afford a mixture of the reduction product norbornane (9) and the ether 10, with the former predominating from bromide 8b and the latter from iodide 8a. The reduction product 9 arises via abstraction of a hydrogen atom by 1-norbornyl radical from the medium and ether 10 via nucleophilic trapping of the 1 -norbornyl cation. Irradiation of either hahde in CH3OD afforded ether 10 with no detectable incorporation of deuterium, indicating that it does not arise via acid-catalyzed addition of the alcohol to an initially formed unsaturated intermediate such as the bridgehead alkene 12 or the propeUane 13. 

Since they are difficult to form, bridgehead cations are highly reactive. Irradiation of hahdes 8 in a variety of media provided a convenient means of exploring the remarkable reactivity of the 1-norbornyl cation (18). It was efficiently trapped by diethyl ether and THE to afford the ethers 19 and 20. Even in aqueous THE, a substantial portion of the butenyl ether 20 was obtained. Trapping by t-butyl alcohol afforded some of the ditertiary ether 21 but was accompanied by formation of 1-norbornanol (22) and 2-methylpropene. Cation 18 was trapped by CHjClj to afford chloride 23, and in aqueous CH3CN the Ritter product 24 was formed. It should be noted that radical abstraction from CH2CI2 occurs at H and ionic abstraction at CL... 

By contrast, the 2-norbornyl cation is easily formed. Moreover, the 2-norbornyl system can readily undergo elimination. On irradiation in CH3OH or (CH3)5COH, the 2-norbornyl iodides 64a underwent exo,endo equilibration and afforded the 1,2- and 1,3-elimination products 66 and 67, along with the nucleophilic trapping product 68. > The corresponding bromides 64b each afforded the same products, along with small amounts of the radical products 65 and 9, but underwent no detectable interconversion. 

The properties of the 7-norbornyl (18), 7-nobomenyl (19), and 7-norboma-dienyl (20) ions and radicals have aroused much interest in view of the evidence that the cations 19 and 20 have nonclassical -complex structures. We... 

The final investigation of the distance dependence of ET dynamics in norbornyl-ogous bridged systems involved photoinduced charge shift ET in 25(4) and 25(6) which possess the A -methylpyridinium acceptor (Figure 25) [79]. Local excitation of the DMN donor results in charge shift to form the distonic radical cation, e.g., 26(4) from 25(4). From the ET rates for the two dyads, an approximate damping factor of... 

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