Structural Relaxation and H Bonding in Isomeric Octanols and Their LiCl Solutions by Calorimetry

Isomeric octanols show a variety of dielectric behavior. At low temperatures, some behave as nonpolar liquids, others as polar liquids. This results from the extent of steric hindrance for intermolecular H bonding when the CH 3 group is in the proximity of the OH group in the seven-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 transition temperature T g, configurational contribution to the heat capacity Δ C p, and distribution of structural relaxation times parameter β. T g of the isomers of octanols lies between 148 and 168 K, Δ C p between 35 and 82 kJ/mol, and β between 0.33 and 0.93. Those octanols that behave dielectrically as nonpolar liquids have a broader distribution of relaxation times, or lower β, than those isomers that behave dielectrically as highly polar liquids. Addition of 5 mol % LiCl increases T g and Δ C p in the former case but decreases both in the latter case, and the distribution of relaxation times broadens in both cases. An analysis in terms of configurational contributions to C p shows that steric hindrance of the OH group determines the H-bonded motifs formed in liquid octanols near their glass−liquid transition temperature.