Laser flash photolysis carbocation generation

When the carbocations are generated by Laser flash photolysis, the ion pair collapse with the nucleophilic counterion Cl- is so fast [136] that the decay cannot be followed with the instrumentation used for these experiments, i.e., only those carbocations which manage to escape from the [Aryl2CH + Cl ] ion pair can be observed. Consequently, all rate constants determined for the Laser photolytically produced carbocations refer to the reactions of the nonpaired entities. 

Triplet-excited nitrobenzyl acetals 18-19 were proposed to undergo direct carbon-carbon bond photoheterolysis to generate the nitrobenzyl carban-ion and the corresponding a-dialkoxy carbocation [Eq. (7)] [81,82]. Transient spectra obtained following laser flash photolysis of 19 showed the formation of the /7-nitrobenzyl anion and the oxocarbocation [83] ... 

Both the 9-methyl and 9-trifluoromethyl-9-fluorenyl cations (7 and 8) have been generated by laser flash photolysis of corresponding alcohol precursors. The product ions were then studied by time-resolved spectroscopy. Consistent with previous studies related to carbocation-bearing electron-withdrawing groups, ion (8) exhibits a significant bathochromic shift in the UV absorption compared to (7). The ions were quenched with methanol and reaction rates showed cation (8) to be a more reactive species. 

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