Some Observations on the Structures of Liquid Alcohols and Their Heats of Vaporization

From comparisons of the differences in heats of vaporization of alcohols (ROH) and their analogous hydrocarbons (RCH 3 ) which turned out to be 6.1 ± 0.1 kcal/mol at 298 K it was concluded that this difference represents the contribution of the hydrogen bond to the value of Δ H vap (alcohol, 298 K). It is further concluded that alcohols are self associated in pure liquids in cyclic clusters each of four alcohols. These conclusions are supported by extensive, earlier studies of PVT relations in vapors, heat capacities, and IR spectra in solutions. Group additivity tables of Ducros et al. are shown to be in excellent agreement with directly measured Δ H vap (298 K) for both alcohols and alkanes. Similar analysis of amines shows a much weaker H-bond with a lower limit of about 2.2 kcal/mol between amines so that amines exist mostly as monomers. Scattered data on diols of lesser accuracy suggest compact sandwich structures with the hydrocarbon tying together two cyclic tetramer rings of H-bonded oxygen atoms.