STRUCTURAL RELAXATION AND H-BONDING IN ISOMERIC OCTANOLS AND THEIR LICL SOLUTIONS BY CALORIMETRY

Isomeric octanols show a variety of dielectric behavior. At low temper atures, some behave as nonpolar liquids, others as polar liquids. This results from the extent of steric hindrance for intermolecular H bond ing when the CH3 group is in the proximity of the OH group in the seve n-membered -C-C- chain. Differential scanning calorimetric studies of nine isomeric octanols and LiCl solutions of two of them are reported here. These are discussed in terms of structural relaxation, glass tra nsition temperature T-g, configurational contribution to the heat capa city Delta C-p, and distribution of structural relaxation times parame ter beta. T-g of the isomers of octanols lies between 148 and 168 K, D elta C-p, between 35 and 82 kJ/mol, and beta between 0.33 and 0.93. Th ose octanols that behave dielectrically as nonpolar liquids have a bro ader distribution of relaxation times, or lower beta, than those isome rs that behave dielectrically as highly polar liquids. Addition of 5 m ol % LiCl increases T-g and Delta C-p, in the former case but decrease s both in the latter case, and the distribution of relaxation times br oadens in both cases. An analysis in terms of configurational contribu tions to C-p, shows that steric hindrance of the OH group determines t he H-bonded motifs formed in liquid octanols near their glass-liquid t ransition temperature.