9-Fluorenyl cation laser flash photolysis

The transient zwitterion (15), obtained from the /(-hydroxy acid precursor by laser flash photolysis, has been characterized 46 it reacts with nucleophiles more slowly than does the 9-fluorenyl cation itself. The parent acid was also characterized.46 Evidence has been presented that (16) undergoes substantial El elimination via a primary carbocation.47 An analysis of solvolysis results for (17) is indicative of extensive charge delocalization throughout the fluorenyl ring at the transition state apparently... 

The photoisomerisation kinetics and other properties of the 1 1 inclusion complexes formed between aromatic derivatives of norbomadiene and P-cyclo-dextrin have been measured." (S)- or (R)-2-Chloropropiophenone affords partially racemised (S)- or (R)-2-phenylpropionic acid respectively by a photo-induced rearrangement via what is probably an ion or radieal intermediate," and (Z)-N-substituted benzoyl-a-dehydrophenylalanines such as (7) are photo-isomerised to 1-azetidine derivatives (8) by a 1,3-acyl migration. Irradiation of 9,9 -bifluorene-9,9 -diol (9) gives a mixture of fluoren-9-one and spiro[9H-fluorene-9,9 (10 -H)-phenanthren]-10 -one (10) whose composition is solvent dependent with the more polar solvents favouring (10). Laser flash photolysis shows the presence of two transients, one of which can be identified with the 9-fluorenyl cation (11), and which originates from photoheterolysis of the diol (9). There is also evidence to support the view that unimolecular rearrange-... 

Carbon-oxygen bond heterolysis is responsible for the observed photolyses of 9-aryl-9-xanthenols ° and llH-benzo[b]fluoren-11-ol. - - Evidence for the formation of the 9-fluorenol radical cation as well as the 9-fluorenyl cation has been obtained from a laser flash photolysis study of 9-fluorenol. 1, l-Di-2-thienylethanol undergoes light-induced dehydration to give i,i-di-2-thienylethylene.Single electron transfer pathways, however, are implicated in the ring cleavage reactions of a,j8-epoxy ketones in the presence of allyltributyltin - or alkylamines. 

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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