Carbocations bicyclo octyl

The activation energies for the fragmentation of the carbene in CH2C12 were calculated by the B3LYP/6-31G method to be 14.6, 2.2, and —0.95 for the bicyclo[2.2.1]heptyl, bicyclo[2.2.2]octyl, and adamantyl systems, respectively. Are the product trends consistent with these computational results, which presumably reflect the relative stability of the carbocation formed by the fragmentation ... 

The carbocation (53), formed under super-acid conditions from the phenyl-substituted tetracyclic alcohol (50), appears to be destabilized relative to (52), formed from (49) under similar conditions. Thus, for example, (53) could only be formed from (50) in FSO3H-SO2CIF at below — 100 "C, whereas (52) can be studied at — 50 °C. Above that temperature rearrangement occurs to give a pair of bicyclo-[3,3,0]octyl allylic cations. Shift data on (53) indicate that the methyl-bearing carbon aioms at the base of the pyramid are more electron deficient than their counterparts... 

Charton used his LDR and related equations in the correlation analysis of solvolytic rate constants for 2-exo- and 2-cndb-norbomyl derivatives [(7) and (8), respectively], substituted in positions 1, 4, 5-exo, 6-exo, 6-endo, or 1-anti A delocalized (resonance) electronic effect was found for all but the 4-substituted derivatives. It was suggested that the transition state resembles a classical carbocation rather than the nonclas-sical norbornyl carbocation. Similar treatments for adamantyl and bicyclo[2.2.2]octyl systems found much less indication of a delocalized effect. 

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