Dielectric studies of molecular association. Concentration dependence of dipole moment of 1-octanol in solution

Abstract

The permittivities at 2 MHz and 25°for 1-octanol in carbon tetrachloride, benzene, and cyclohexane solutions have been measured over the entire alcohol concentration range, with particular attention being paid to the range below 0.1 M. By use of the Kirkwood-Frohlich equation the apparent dipole moment of the alcohol as a function of concentration has been evaluated; using this concentration dependence and infrared absorption results, the natures of the proposed associated species are considered. Equilibrium constants have been determined for a monomer-dimer-trimer equilibrium model of the alcohol self-association at low concentrations; the association follows a general pattern: monomer-small, high dipole moment polymer-low dipole moment cyclic polymer-high dipole moment polymers.

The Association of 3‐ethylpentanol‐3 in Carbon Tetrachloride from the Static Dielectric Permittivity and the Infrared Absorbance

“…In principle values of C, can be obtained from the infrared absorbance in the hydroxyl stretching range. The general features of the spectra are in agreement with those described in the literature [2,5,61. The monomer peak, the only peak present at the lowest concentrations, has a frequency of 3620 cmslightly decreasing at decreasing temperature (3620 cm-' at 25"Cand 3617 c m -' a t -2O'C).Thedependenceofthisfrequency on the concentration is not very clear from our measurements but in the measured temperature and concentration range the differences d o not exceed 1 cm-This peak shows even at the lowest concentrations a shoulder at the low frequency side (at about 3610cm-') with an absorbance that seems to increase relative to the maximum with decreasing temperature and increasing concentration.…”

“…where BE is the difference between the dielectric constant of solution and solvent, has the same shape [2]. It appears from this figure that at low concentrations within the accuracy of the measurements (pz)app is independent of the concentration.…”

“…at 25 "C due to the appearance of multimers with a great dipole moment. In view of the similar shape of the 1R spectrum [5, 61 and the (p2)app versus x plot [2,3,8,9] for different alcohols in alkanes and carbon tetrachloride at low concentrations we can probably extend the applicability of this model to other alcohols in alkanes and carbon tetrachloride in the low concentration range.…”

Ultrasonic and13C N.M.R. studies of isomeric octanols

“…A comparison of the values of the enthalpy differences obtained from this study and those determined by dielectric measurements [17,18] indicates that there is a considerable difference between the values. Similar observations have been made when comparing the values observed for the enthalpy difference associated with internal rotational processes determined by infrared spectroscopy and by acoustics; they have been attributed to the efforts of a relaxing contribution from volume changes associated with the conformational equilibrium.…”

“…The differences observed between 2,3-dimethyl-and 2,4-dimethyl-3-hexanol are comparable to those observed in the related hydrocarbons. It has been inferred from dielectric measurements [18,19] that these alcohols tend to prefer a linear rather than a ring association. The values of the activation energy observed for the structural process, are approximately two hydrogen bonds being broken in the process, such an observation is consistent with either relaxation scheme.…”