Molecular association and dynamics in n-pentanol and 2-methyl-2-butanol

Abstract

Static dielectric constant, viscosity, density, ultrasonic and dielectric relaxation measurements are reported for two pentanol isomers (n-pentanol and 2-methyl-2-butanol) in a wide range of temperatures. The results show a different extent of H-bonds self-association in relation to the molecular geometry of the alcohol. The activation energies obtained from dielectric and ultrasonic studies are compared with those obtained from viscous flow. Such a comparison, together with the analysis of all the dielectric and ultrasonic relaxation data, show that in n-pentanol a correlation between viscosity and ultrasonic relaxation exists, while dielectric relaxation is not correlated with the other two processes. This finding has been rationalized in terms of different mechanisms. In 2-methyl-2-butanol a correlation between ultrasonic and dielectric relaxation processes has been observed. Additional contribution of ultrasonic absorption associated with isomeric internal rotational of the molecules has been assumed to explain the experimental data for this alcohol.