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

The dipole moments of ((plus-minus))-(1,1ʹ-biindene)-3,3ʹ-dione 1, ((plus-minus))-2,2ʹ,3,3ʹ-tetrahydro-(1,1ʹ-binaphthalene)-4,4ʹ(1H,1ʹH)-dione 2, and ((plusminus))-(1,1ʹ-bibenzosuberene)-5,5ʹ-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.