The Dipole Moments of α,ω-Alkanediols

Abstract The electric dipole moments of α,ω-alkanediols such as HO–(CH2)n–OH (n being varied from 2 to 5) were measured both in dioxane and in a mixed solvent of dioxane with carbon tetrachloride at 25°C. The observed dipole moments increase with the increasing n until n=4, and then decrease for n=5, while the calculated dipole moments based on the vector addition of group moments on the assumption of the random coil model for alkane chains increase monotonously as n increases from 2 to 5. It is concluded that for both propanediol and butanediol the conformations forming the intramolecular hydrogen-bond which have the larger dipole moments contribute appreciably to the observed dipole moments. The dipole moment of pentanediol is close to the calculated one for the random coil model, whereas that of ethylene glycol suggests the existence of the intramolecular hydrogen-bond. Population analysis of the hydrogen-bonded species in solutions is also given.