EFFECT OF IONS ON INTERMOLECULAR ASSOCIATION AND SUB-TG DIELECTRIC-RELAXATION IN ISOMERIC OCTANOLS

The effect of ions on the H-bond association in 4-methyl-3, 2-methyl-1, and 2-methyl-6-heptanols has been studied from measurements of their dielectric properties in their pure state and their LiClO4 solutions over a temperature range from their glassy to a supercooled fluid state. The ions increase the equilibrium permittivity of 4-methyl-3 and decrease that of 2-methyl-1 and 2-methyl-6-heptanols. Ionic interaction breaks H bonds in their structures and converts ring dimers of virtually zero dipole moment to linear dimers or monomers for the 4-methyl-3 and converts chain n mers to shorter chains for the 2-methyl-1, and 2-methyl-6-heptanols, thus confirming our earlier interpretation of two types of H-bond association in isomeric octanols. The effect of ions on the permittivity and H-bond structure of 4-methyl-3 is similar to the effect of hydrostatic pressure and on those of similar to the effect of hydrostatic pressure and on those of 2-methyl-1 and 2-methyl-6-heptanols is opposite to that of hydrostatic pressure. On the addition of LiClO4, the height of the sub-T(g) relaxation peak increases as does the permittivity at 100 K. The former is a reflection of less efficient molecular packing and the latter of an increase in the optical and infrared polarizabilities with increase in the LiClO4 concentration. Dielectric and conductivity measurements of ionic solutions are useful methods for studying the H-bond association in pure liquids.