Irradiation of 9,9'-bifluorene-9,9'-diol (1) gave 9-fluorenone and spiro[9H-fluorene-9,9'(10'-H)-phenanthren]-10'-one (4), the latter arising from a pinacol rearrangement. The distribution of fluorenone and ketone 4 was solvent dependent with the latter being the major product in trifluoroethanol, a solvent known to stabilize carbocation intermediates. Laser flash photolysis of diol 1 in 2,2,2-trifluoroethanol or hexafluoro-2-propanol showed two transients absorbing at 350 and 505 nm with a weak band at 700 nm. The latter two peaks are assigned to the corresponding substituted 9-fluorenyl cation (5) formed from photoheterolysis of diol 1. Comparison of the decay kinetics between cation 5 and other 9-fluorenyl cations, the parent 9-fluorenyl and 9-phenyl-9-fluorenyl cations, showed that the decay of 5 was relatively insensitive to the nature of the solvent as compared to the latter two carbocations suggesting that unimolecular rearrangement in 5 competes with nucleophilic quenching.

The aromatic protons and carbons in the NMR spectra of certain clamped 1,1,2,2-tetraarylethane-1,2-diols undergo intermediate exchange at ambient temperature as the result of conformational equilibrium between two enantiomeric gauche forms. The crystal structures for two of these derivatives show the conformational preference for this geometry in the solid state in contrast to other reported unclamped 1,1,2,2-tetraarylethane-1,2-diols. The conformational preference of these vicinal diols parallels that for the 1,1,2,2-tetraarylethanes. However, in the asymmetrically substituted diphenylmethylfluorene series, the vicinal diol prefers to adopt a gauche conformation in contrast to the hydrocarbon which prefers the anti geometry attributed to hydrogen bonding effects in the former. The results of AM1 calculations for the conformational preferences of this series of diols and ethanes are included and agree with experimental observations.

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