Rotational isomerism in 1,1′-dinitrobicyclopentyl, 1,1′-dinitrobicyclohexyl and 1,1′-dinitrobicycloheptyl

Abstract

IR and Raman spectra of 1,1′-dinitrobicyclopentyl, 1,1′-dinitrobicyclohexyl, and 1,1′-dinitrobicycloheptyl in the solid and solution states are reported and assignment of frequencies made. Dipole moments in different solvents (benzene, carbon tetrachloride, and cyclohexane) at different temperatures and molar Kerr constants (in carbon tetrachloride and benzene) are also reported. Analysis of the relative permittivity data shows that, at 25°C, the compounds in the series exist as rotameric mixtures in carbon tetrachloride solution containing 83, 42, and 16% respectively of the gauche rotamer. Benzene causes the gauche population to increase, as evidenced by dipole moment and Kerr-constant values in this solvent. The experimentally derived values of the energy difference between gauche and trans rotamers, the dihedral angle of the gauche rotamer, and the gauche/trans population quotients are compared with values predicted by the semiempirical MO program AMPAC. Comparison of the Raman and IR spectra of the solids suggests that all three compounds exist in the gauche conformation in the solid state.