Crystal structure of and conformational equilibria in 1,1 '-dihydroxybis (4H-cyclopenta[def]phenanthrene) and related derivatives

The aromatic protons and carbons in the NMR spectra of certain clamped 1,1, 2,2-tehaarylethane-1,2-diols undergo intermediate exchange at ambient tempe rature 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 conform ational preference of these vicinal diols parallels that for the 1,1,2,2-te traarylethanes. However, in the asymmetrically substituted diphenylmethylfl uorene series, the vicinal diol prefers to adopt a gauche conformation in c ontrast to the hydrocarbon which prefers the anti geometry attributed to hy drogen bonding effects in the former. The results of AM1 calculations for t he conformational preferences of this series of diols and ethanes are inclu ded and agree with experimental observations. Copyright (C) 2001 John Wiley & Sons, Ltd.