Conformational Analysis of (±)-(1,1′-Biindene)-3,3′ -dione, 2,2′,3,3′-Tetrahydro-(1,1′-binaphthalene)-4,4′ (1H,1′H)-dione, and (1,1′-Bibenzosuberene)-5,5′-dione

Abstract

The dipole moments of (±)-(1,1′-biindene)-3,3′-dione 1, (±)-2,2′,3,3′-tetrahydro-(1,1′-binaphthalene)-4, 4′(1H,1′H)-dione 2, and (±)-(1,1′ -bibenzosuberene)-5,5′-dione 3 in carbon tetrachloride and benzene were measured over a range of temperatures. Analyses of the relative permittivity data in carbon tetrachloride and benzene showed that at 25 °C, 1 exists predominantly in the gauche conformation, whilst 2 and 3 favor the trans form. The experimentally derived values of the energy difference between the gauche and trans rotamers and the gauche/trans population quotient were compared with values predicted by molecular-orbital calculations. The crystal and molecular structures of 2 and 3 were determined by single-crystal X-ray diffraction methods. Both compounds exist in the trans conformation in the solid-state. Dynamic 1H NMR was employed to 3 in order to determine the activation parameters for the barriers to rotation in solution.