CONFORMATIONAL INVESTIGATION OF N-ARALKYL-BISPYRIDINIUM DICATIONS BY THE COTTON MOUTON EFFECT METHOD

Molar Cotton-Mouton constants and refractions are reported at 298 K for the following N-aralkyl-bispyridinium dications as solutes in water: 1,3-(CH2+NC5H5)2C6H4, 1,3-(CH2+NC5H4-2'-Me)2C6H4, 1,3-(CH2+NC5H5)2-4,6-Me2C6H2, 1,3-(CH2+NC5H4-2'-Me)2-4,6-Me2C6H2, 1,3-(CH2+NC5H5)2-2,4,6-Me3C6H and 1,4-(CH2+NC5H5)2-2,5-Me2C6H2. The data are analyzed in terms of the preferred conformations adopted by the cations in solution. The experimental data are consistent with the presence, in solution, of helical structures, where all pyridinium and aryl rings are twisted in the same direction with respect to the C(Ar)-CH2-N(Ar) reference plane. In the case of the first four compounds listed above, the preferred conformers possess a spiral spatial arrangement of the three aryl rings along a screw line. For the last compound of this series, a mixture of different conformers seems to be populated in the ground state.